6464ak en ado net beta trainermanual

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6464A Visual Studio 2008®: ADO.NET

Be sure to access the extended learning content on your Course Companion CD enclosed on the back cover of the book.

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ii Visual Studio 2008®: ADO.NET

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Visual Studio 2008®: ADO.NET iii

Contents

Module 1: Getting Started with ADO.NET Lesson 1: Introduction to ADO.NET 3.5 1-3

Lesson 2: Connecting to a Database and Retrieving Data 1-7

Lesson 3: Best Practices for Managing Connections and Performing Queries 1-15

Lab: Connecting to a Database and Retrieving Data 1-22

Module 2: Modifying Data by Using ADO.NET Commands Lesson 1: Inserting, Updating and Deleting Data 2-3

Lesson 2: Managing Data Integrity and Concurrency 2-8

Lab: Modifying Data by Using ADO.NET Commands 2-14

Module 3: Querying and Maintaining Data by Using DataSets Lesson 1: Creating and Using a DataSet to Retrieve Data 3-3

Lesson 2: Updating a Database by Using a DataSet 3-10

Lesson 3: Using a DataSet in an Occasionally Connected Environment 3-16

Lab: Querying and Maintaining Data by Using DataSets 3-19

Module 4: Querying and Maintaining Data by Using LINQ Lesson 1: Querying In-Memory Data by Using LINQ Query Expressions 4-3

Lesson 2: Retrieving Data by Using LINQ to SQL 4-9

Lesson 3: Modifying Data by Using LINQ to SQL 4-16

Lab: Querying and Maintaining Data by Using LINQ to SQL 4-20

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iv Visual Studio 2008®: ADO.NET

Module 5: Implementing an Entity Data Model by Using the ADO.NET Entity Framework

Lesson 1: Creating an Entity Data Model by Using the ADO.NET Entity Framework 5-3

Lesson 2: Querying and Modifying Data by Using the ADO.NET Entity Framework 5-9

Lab: Implementing an Entity Data Model by Using the ADO.NET Entity Framework 5-17

Module 6: Building Occasionally Connected Solutions by Using Synchronization Services

Lesson 1: Understanding Microsoft Synchronization Services 6-3

Lesson 2: Downloading Data by Using Synchronization Services 6-7

Lesson 3: Uploading Data by Using Synchronization Services 6-12

Lab: Building Occasionally Connected Solutions by Using Synchronization Services 6-17

Course Evaluation 6-33

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About This Course This section provides a brief description of the course, audience, suggested prerequisites, and course objectives.

Course Description This two-day instructor-led course describes the key features of application development with Microsoft® database development technologies, including Microsoft Visual Studio® 2008 and Microsoft ADO.NET 3.5. It explains how to develop an application that can insert, delete, and update database records in both a connected and occasionally connected scenario.

Audience This course is intended for application developers. You should know how to build windows forms and how to use the common features of the base class library. You should have a basic understanding of Relational Database Management System databases and Transactional Structured Query Language. You do not have to understand concepts such as advanced UI threading and asynchronous programming. You also do not require experience building Visual Studio add-ins or custom designers.

Student Prerequisites In addition to your professional experience, students who attend this training should have technical knowledge equivalent to the following:

Intermediate experience of application development by using previous versions of Microsoft Visual Studio. (Level 200).

Course Objectives After completing this course, you will be able to:

• Use ADO.NET commands to insert, delete and modify database records.

• Use Datasets to access tables in an occasionally connected application.

• Use Language-Integrated Query (LINQ) to insert, delete and modify database records.

• Use the Entity Framework for ADO.NET and Entity SQL to develop code that insert, delete, and modify entities in a conceptual model.

• Use Synchronization Services to insert, delete, and modify records in an occasionally connected application.

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Course Outline This section provides an outline of the course:

Module 1, "Getting Started with ADO.NET 3.5". This module introduces ADO.NET and describes how to connect to a database and how to use ADO.NET commands to retrieve data. It shows how to use simple commands and commands with parameters.

Module 2, "Modifying Data by Using ADO.NET Commands". This module describes how to use ADO.NET commands to insert, delete, and modify database records. It shows how to perform commands asynchronously, and under a transaction.

Module 3, "Querying and Maintaining Data by Using DataSets". This module describes how to access and manipulate data by using a DataSet. It shows how to create a typed DataSet and how to use a DataSet in an occasionally connected scenario.

Module 4, "Querying and Maintaining Data by Using LINQ". This module describes the capabilities of LINQ and how to use LINQ to query and modify data.

Module 5, "Implementing an Entity Data Model by Using the ADO.NET Entity Framework". This module describes the conceptual and logical models of data and how to map between the two. It explains how to use Entity SQL to access data through the entity model.

Module 6, "Building Occasionally Connected Solutions by Using Synchronization Services". This module describes how to use Synchronization Services to synchronize a local database cache on an occasionally connected application with a database server.

Course Materials The following materials are included with your kit:

• Course Handbook. The Course Handbook contains the material covered in class. It is meant to be used in conjunction with the Course Companion CD.

• Course Companion CD. The Course Companion CD contains the full course content, including expanded content for each topic page, full lab exercises and answer keys, topical and categorized resources, and Web links. It is meant to be used both inside and outside the class.

Note: To access the full course content, insert the Course Companion CD into the CD-ROM drive, and then in the root directory of the CD, double-click StartCD.exe.

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• Course evaluation. At the end of the course, you will have the opportunity to complete an online evaluation to provide feedback on the course, training facility, and instructor.

To provide additional comments or feedback on the course, send an e-mail to [email protected]. To inquire about the Microsoft Certification Program, send an e-mail to [email protected].

Virtual Machine Environment This section provides the information for setting up the classroom environment to support the business scenario of the course.

Virtual Machine Configuration In this course, you will use Microsoft Virtual Server 2005 R2 SP1 to perform the labs.

Important: At the end of each lab, you must close the virtual machine and must not save any changes. To close a virtual machine without saving the changes, perform the following steps: 1. On the host computer, click Start, point to All Programs, point to Microsoft Virtual Server, and then click Virtual Server Administration Website. 2. Under Navigation, click Master Status. For each virtual machine that is running, right-click the virtual machine name, click Turn off Virtual Machine and Discard Undo Disks, and then click OK.

The following table shows the role of each virtual machine used in this course.

Virtual machine Role

6464A-XX

(where XX represents the module number

Application development computer

Software Configuration The following software is installed on each virtual machine:

• Windows Vista® Enterprise

• Microsoft Visual Studio 2008

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• Microsoft SQL Server® 2005 Express Edition

Course Files There are files associated with the labs in this course. The lab files are located in the folder E:\Labfiles on the student computers.

Classroom Setup Each classroom computer will have the same virtual machine configured in the same way. The virtual machines do not need to be connected to a network.

Course Hardware Level To ensure a satisfactory student experience, Microsoft Learning requires a minimum equipment configuration for trainer and student computers in all Microsoft Certified Partner for Learning Solutions (CPLS) classrooms in which Official Microsoft Learning Product courseware is taught.

This course requires that you have a computer that meets or exceeds hardware level 5, which specifies a 2.4-gigahertz (GHz) (minimum) Pentium 4 or equivalent CPU, at least 2 gigabytes (GB) of RAM, 16 megabytes (MB) of video RAM, and a 7200 RPM 40-GB hard disk.

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ITED Getting Started with ADO.NET 3.5 1-1

Module 1 Getting Started with ADO.NET 3.5

Contents: Lesson 1: Introduction to ADO.NET 3.5 1-3

Lesson 2: Connecting to a Database and Retrieving Data 1-7

Lesson 3: Best Practices for Managing Connections and Performing Queries 1-15

Lab: Connecting to a Database and Retrieving Data 1-22

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ITED1-2 Visual Studio® 2008: ADO.NET

Module Overview

ADO.NET is a collection of Microsoft® .NET Framework classes that provide data access services for relational, XML, and application data. These classes abstract the data access through strongly typed data provider classes, or through generic interfaces and classes.

ADO.NET also provides data binding classes for Microsoft ASP.NET, Windows Forms applications, and Windows® Presentation Foundation (WPF) applications. Microsoft Visual Studio® 2008 provides designers for creating data access controls.

This module describes how to use ADO.NET to connect to a database and read data from that database. The module also describes how to handle connection exceptions.

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Lesson 1 Introduction to ADO.NET 3.5

ADO.NET is a collection of classes that connect to a database, perform actions on the database, and retrieve data from the database. A collection of such classes is called a data provider and is used to access data from a specific data source. In addition to the fundamental classes for accessing data through a data source, the .NET Framework also provides language features and class libraries that use ADO.NET to further abstract data access.

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What Is ADO.NET 3.5?

Key Points ADO.NET is a collection of classes that enables you to access data in a data source. A data provider is a collection of ADO.NET classes that enable you to access data from a specific data source. ADO.NET provides classes that access data through disconnected datasets and also supplies data binding to controls.

Question: When you would use data through a data provider connection, and when would you use disconnected data?

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.NET Framework Data Providers

Key Points ADO.NET includes .NET Framework data providers that enable you to connect to a database, execute commands, and retrieve results. The .NET Framework data providers create a minimal layer between the data source and your code, which increases performance and does not sacrifice functionality.

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ADO.NET 3.5 Technologies and Techniques

Key Points ADO.NET 3.5 is a collection of classes that is part of the .NET Framework library. In addition, Visual Studio 2008 provides tools that use ADO.NET classes in your code, and Visual C# and Visual Basic have language features for embedding data access in code. In addition, Visual Studio 2008 designers generate ADO.NET code for you.

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Lesson 2 Connecting to a Database and Retrieving Data

This lesson shows how to create a connection to a data source, issue a command, and then retrieve the data by using typed classes for the SQL Server data provider.

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Connecting to a Database

Key Points To create a connection you use one of the connection classes that implement IDbConnection and supply a connection string. To create the connection, you then call Open.

Because connection objects hold limited resources, when you have finished with a connection object, you must release those resources. To do this, you can call the Dispose method on the object to release it. You can also call the Close method or use the object in a Using statement (Visual Basic) or a using statement (Visual C#).

Question: Why is the Using statement important, and what problems might you experience when you use it?

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Handling Connection Exceptions

Key Points Two types of exceptions can be generated when you open a connection: InvalidOperationException exception object is generated by the data provider on the client computer and SqlException exception object contains errors that are generated by the data source on the server.

Question: Can you identify some of the error conditions that are returned through SqlException exception object?

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Executing a Query and Retrieving the Results

Key Points To retrieve data from a database, you must create a command object, initialize it with information about the command, and then execute the command. If the command returns results, you obtain a resultset through a DbDataReader object (for the SQL Server data provider this is a SqlDataReader object). To populate the DbDataReader object with the next row, you call the Read method and then you can call members to obtain the columns of this row. You must close the DbDataReader object after you have finished using it.

Question: Why do you think it is important that you close the DbDataReader object after you have finished using it?

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Mapping SQL Server Data Types to .NET Framework Types

Key Points Data sources have their own data types and when you execute a command the results that are returned use those data types. To make data useful for your code, it must be converted into .NET Framework data types. The data provider classes derived from the DbDataReader and DbParameter classes perform these conversions for you.

Question: Why do data sources have different data types?

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Handling Exceptions when Retrieving Data

Key Points The SqlCommand command is not executed until the Read method is called the first time, so if there is an error in the command you only receive these when the Read method is called. If you perform an asynchronous call you must open the SQL Server connection specifically to support asynchronous calls, however, if you omit to do this the exception only occurs when the first asynchronous call is attempted on a data reader object. You receive errors from the data source in a SqlException exception object which has a collection of SqlError objects: one for each SQL Server error generated.

Question: When you execute a command at what point in your code may exceptions be thrown?

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Disconnecting from a Database

Key Points A connection object holds a connection to the data source. The data source connection is a scarce resource and therefore you should only maintain this connection for as little time as necessary. To do this you should ensure that when you have finished using a connection you call the Close method.

Question: What is the difference between the Dispose and Close method? When would you use each one?

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Demonstration: Connecting to a Database and Retrieving Data

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Lesson 3 Best Practices for Managing Connections and Performing Queries

ADO.NET provides additional features to improve how you connect to a database and access data in that database. You can:

• Store the connection string in a configuration file for better maintainability.

• Use connection pooling for more efficient use of connections.

• Use asynchronous calls to ensure responsiveness.

• Perform commands that use parameters and commands that return single values.

• Write generic data access code.

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Storing Connection Strings in a Configuration File

Key Points The connection string determines which server and which database you connect to, so if you hard code this into your application, the database cannot be renamed, nor can you move the database to another computer. You can store the connection string in a separate file.

Question: What are the advantages and disadvantages of using a configuration file?

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Managing Database Connections

Key Points Database connections are expensive resources to create. If your application uses many connections then it makes sense to reuse them. To cut down on the time taken to create connections, the SQL Server data provider uses a connection pool. When you create a connection it is put into the pool and when your code closes a connection the connection is not closed, but instead the entry in the pool is marked as free so that it can be reused. The best way to use pooled connections is to open connections as late as possible and close them as early as possible.

Question: What resources do you think are consumed by database connections?

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Executing Long-Running Queries Asynchronously

Key Points Commands that are involved with an inter-process call may also involve a call to another computer: this takes time and means that the thread is blocked until the command completes. This means that the calling thread cannot do any work, which is catastrophic if the calling thread is the main thread in a Windows Forms application because it means that Windows messages are not be handled. You can prevent this from happening by calling the command asynchronously, by creating a connection that supports asynchronous calls.

Question: What happens to your Windows Forms application if Windows messages are not handled?

Question: Why would you use the SQL Server asynchronous methods rather than calling a delegate asynchronously?

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Executing Single-Value Queries Efficiently

Key Points It is important that you close various data provider objects such as the connection object and the data reader object. If the command returns a single (or no) value then it is easy to forget to close objects like the data reader. The DbCommand class has methods that wrap the ExecuteReader method so that it hides the DbDataReader object and ensures that this object is closed before the wrapper method returns.

Question: What examples of commands can you think of that only return a single value?

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Creating and Executing Parameterized Commands

Key Points Parameterized commands are useful for two reasons. First, if you call a parameterized command several times, data sources can recognize these as being the same command and optimize its execution. Second, they help to prevent SQL injection attacks.

Question: When are you likely to use parameterized commands?

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Writing Provider-Independent Code in ADO.NET

Key Points Each data provider must supply a DbProviderFactory class that you can use to create data provider objects for the data provider. You use references to the provider-independent abstract base classes and so that your code is generic even though the actual objects are specific to the data provider.

Question: Under what circumstances would data provider agnostic data access code be used?

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Lab: Connecting to a Database and Retrieving Data

Exercise 1: Connecting to a Database

Scenario You are a developer for the Medical Clinic Management System for Contoso, Ltd. The Contoso Clinic Management System is a healthcare system for hospitals and clinics that run specialist practices. The clinic must organize a set of consultants and equipment to service patient needs. Patients are referred to the clinic from their Family Practitioner or General Practitioner. The system supports both the management of appointments and the management of patient information.

In this exercise, you will develop the code to connect to a database.

The main tasks for this exercise are as follows:

1. Start the 64624A-LON-DEV-01 virtual machine and log on as Student.

2. Open and review the project.

3. Add a connection string to the configuration file.

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4. Add a data access class to the project.

5. Implement the GetConnection method.

6. Build and run the project.

Task 1: Start the 64624A-LON-DEV-01 virtual machine and log on as Student 1. Open the Virtual Server Remote Control Client and double-click 6464A-LON-

DEV-04.

2. Log on to 6464A-LON-DEV-04 as Student using the password Pa$$w0rd.

Task 2: Open and review the project 1. Click Start, point to All Programs, point to Microsoft Visual Studio 2008,

and then click Microsoft Visual Studio 2008.

2. In Microsoft Visual Studio, open the ContosoMedical project from the E:\Labfiles\Starter\VB\ContosoMedical folder (if you are using Microsoft Visual Basic® development system) or E:\Labfiles\Starter\CS\ContosoMedical folder (if you are using Microsoft Visual C#® development tool).

3. In Solution Explorer, open all the projects and examine their contents.

• The ClinicAdminClient project is a Windows Forms project with a single form that enables you to retrieve doctor names from the database.

• The ContosoMedicalDatabases project contains scripts for creating the database. These are here for your information, the database is already installed on the computer.

• The ContosoMedicalUtilities project is a library project that contains the code to access the database.

4. In Solution Explorer, under the ClinicAdminClient project, double-click ClinicAdminForm.vb (Visual Basic) or ClinicAdminForm.cs (Visual C#) to open the form in the forms designer.

5. Review the form:

• Click the Get Count button, to count how many doctors are in the database.

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• Click the Show Doctors button to get either all of the doctors, or just the doctors with a particular specialty.

• Use the specialtyTextBox, when you want a list of doctors who have a particular specialty.

• Click the doctorsListBox, and then click the Show Doctors button to see the retrieved doctors.

Task 3: Add a connection string to the configuration file 1. In Solution Explorer, open the project Properties, and then on the Settings

tab, add a (connection string) setting with these values (the values are single lines):

Column Value

Name ContosoMedicalDBConnectionString

Value Data Source=.\SQLEXPRESS; Initial Catalog=ContosoMedicalDB; Integrated Security=true

2. Save the configuration values.

Note: Saving the values adds an app.config file to the project with the connection string you have just added, however the wizard gives the value a name which enables it to be used with the My.Settings (Visual Basic) or Properties.Settings (Visual C#) class. You will not use these classes, so to make the code easier to read you should rename the value name.

3. Open the app.config file in the editor. Check that the designer has added a <connectionStrings> element and, below that, there is an <add> element with the values that you entered in step 5 of Task 2.

4. Change the name attribute to ContosoMedicalDBConnectionString.

5. Save the changes.

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Task 4: Add a data access class to the project 1. In Solution Explorer, under the ContosoMedicalUtilities project, double-click

ContosoMedicalDAC.vb (Visual Basic) or ContosoMedicalDAC.cs (Visual C#) to open the file in the editor.

Note: The project file is empty (Visual Basic) or has an empty namespace called ContosoMedicalUtilities (Visual C#). You will add the skeleton code for this class from an existing file.

2. Copy the code from Ex1_Task4.txt (in the E:\Labfiles\Starter\VB for Visual Basic or E:\Labfiles\Starter\CS for Visual C#) into the ContosoMedicalDAC source file.

Task 5: Implement the GetConnection method 1. In the ContosoMedicalUtilities project, add a reference for the

System.Configuration assembly.

2. In the ContosoMedicalDAC source file, add a statement so that you can use System.Configuration classes without a fully qualified name.

3. In the GetConnection method, add code that gets the connection string from the configuration file.

• Use the ConnectionStrings collection on the ConfigurationManager class to access the ContosoMedicalDbConnectionString value.

• Use this connection string to initialize a SqlConnection object and return this object from the function.

Task 6: Build and run the project 1. Build the project and run it.

Note: The ContosoMedicalDC.GetAllDoctors method that you copied in Task 4 has been implemented to call GetConnection so that you can test your code. The method does nothing else.

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2. Click Show Doctors and verify that no exceptions are thrown.

Results: After this exercise, you should have created a project that compiles correctly and can call GetConnection without throwing an exception.

Exercise 2: Executing a Simple Query

Scenario In this exercise, you will add code to query the database for the number of doctors in the database. The doctor information is held in the Doctors table, so to get the number of doctors the code should query for the number of rows in this table.


1. Implement the GetNumberOfDoctors method.

2. Implement the handler for the Get Count button.


Task 1: Implement the GetNumberOfDoctors method 1. In Solution Explorer, open the Data Access Component file and scroll down to

the GetNumberOfDoctors method. This method has only enough code so that it compiled in the last exercise.

2. Add code to give result a value. The result value will be the return value from the following query:

select count(*) from Doctors

• Call the GetConnection method to get a connection.

• Create a command to execute the query,

• Execute the command by using the ExecuteScalar method.

• Close the connection.

Task 2: Implement the handler for the Get Count button 1. In Solution Explorer, under the ClinicAdminClient project, double-click

ClinicAdminForm.vb (Visual Basic) or ClinicAdminForm.cs (Visual C#) to open the form in the forms designer.

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2. Double-click the Get Count button, to open the file in code view. The cursor is placed in the getDoctorCount_Click handler method.

3. This method already has a Try (Visual Basic) or try (Visual C#) block for the data access code. Within this block add code to create an instance of the Data Access Component, call GetNumberOfDoctors, and show the returned result in a message box.

Task 3: Build and run the project 1. Build and run the project.

2. Verify that when you click the Get Count button you get a message box and no exceptions occur.

Results: After this exercise, the Get Count button should show a dialog with the number of doctors in the database.

Exercise 3: Executing a Query That Returns a Result Set

Scenario In this exercise, you will implement code to query the database and return a rowset with all of the doctors in the database.


1. Implement the GetAllDoctors method.

2. Implement the ShowAllDoctors method.


Task 1: Implement the GetAllDoctors method 1. In Solution Explorer, open the source file for the Data Access Component and

scroll to the GetAllDoctors method. The implementation in the method was provided so that you could test the results in Exercise 1, and becaue you do not need this code now, delete it.

2. Implement the GetAllDoctors method to return a SqlDataReader object that is the result of the following query:

select DoctorID, FirstName, LastName, Specialty from Doctors

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• Call the GetConnection method to get a connection object.

• Call the ExecuteReader method so that the reader object closes the connection object (CommandBehavior.CloseConnection).

• Return the reader object from the method.

Task 2: Implement the ShowAllDoctors method 1. Open the ClinicAdminClient form in the code editor and scroll down to the

ShowAllDoctors method.

2. This method already has a Try (Visual Basic) or try (Visual C#) block for the data access code. In this block add code to create a Data Access Component and call GetAllDoctors.

3. Iterate through all of the results in the SqlDataReader object that is returned from the GetAllDoctors function and add each result to the list box as strings in the following format:

[DoctorID]\tDr. FirstName LastName, Specialty

Note: For Visual C#, you use \t for the tab character. For Visual Basic you use the Chr(9) function to insert the tab character into the string.

Task 3: Build and run the project. 1. Build and run the project.

2. Verify that, when you click the Show Doctors button:

• No exceptions are thrown.

• On each line of the list box there is the description of each doctor.

Results: After this exercise, you should have an application that can show all of the doctors in the database in the list box.

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Exercise 4: Executing a Query That Requires a Parameter

Scenario In this exercise you will write code to execute a stored procedure in the database. The stored procedure will return all of the doctors that have the specialty provided through a parameter.


1. Review the stored procedure.

2 Review the Doctor class.

3. Implement the GetDoctorsForSpecialty method.

4. Implement the ShowDoctorsForSpecialty method.


Task 1: Review the stored procedure 1. In Solution Explorer, open ContosoMedicalDatabases, open the Create

Scripts node, then double-click ContosoMedicalDB.dbo.uspGetDoctorsForSpecialty to open the stored procedure in the editor.

2. Review the procedure:

• The procedure has one in parameter @specialty.

• The procedure has one out parameter @doctorCount.

• The procedure has a return value that is the number of doctors who have the provided specialty.

• The procedure performs a query for all of the doctors who have the provided specialty.

Task 2 Review the Doctor class • Open the Doctor.vb (Visual Basic) or Doctors.cs (Visual C#) and examine the

code.

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Task 3: Implement the GetDoctorsForSpecialty method 1. In the code file for the data access component, scroll to the

GetDoctorsForSpecialty method. Copy and paste the contents of the Ex4_Task2.txt file (E:\Labfiles\Starter\VB for Visual Basic or E:\Labfiles\Starter\CS for Visual C#) for the implementation of this method.

2. Review the code you have just copied. This code:

• Obtains a connection from the GetConnection method.

• Creates a command to call the uspGetDoctorsForSpecialty stored procedure.

• Initializes the @specialty parameter with the specialty requested.

• Initializes the out parameter @doctorCount and return value parameter.

• Executes the comment and uses the rowset to initialize a List<> object of Doctor objects.

• Initializes the ByRef (out) parameters with return parameter from the command.

• Closes the connection.

Task 4: Implement the ShowDoctorsForSpecialty method 1. In the code file for the ClinicAdminClient form, scroll down to the

ShowDoctorsForSpecialty method and paste the contents of Ex4_Task3.txt (from E:\Labfiles\Starter\VB for Visual Basic or E:\Labfiles\Starter\CS for Visual C#).

2. Review the code you have just copied. This code:

• Creates the data access component.

• Obtains a List<> object of Doctor objects, the number of specialties and the number of doctors with the requested specialty by calling the GetDoctorsForSpecialty method.

• Iterates through the List<> object and adds information about each doctor to the list box.

• Displays a message box with the specialty count and number of doctors who have the requested specialty.

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Task 5: Build and run the project 1. Build and run the application.

2. Verify that there are no exceptions and that the application works as expected:

• Click Show Doctors to fill the list box.

• Choose a specialty from this list and type this text into the Specialty text box.

• Click Show Doctors again and verify that the list box has a description of each doctor who has the specialty that you chose.

Results: After this exercise, the application should list the doctors who have a specialty that you provide.

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Module Review and Takeaways

Review Questions 1. Why was it important to make GetConnection a Private function?

This method creates a connection object and returns it. A class invariant is that every method that calls the GetConnection function must close the connection. Every method in this class obeys this rule. If this function was made Public then you cannot guarantee that callers will close the connection.

2. In GetNumberOfDoctors, why was the connection closed in the Finally clause?

The connection must be closed in this method, regardless of how the method completes. The Finally clause has code that is executed whenever code execution leaves the Try block, regardless of how that happens. So if the Try block has a Return, a GoTo, or even if an exception is thrown, the Finally block is still called.

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3. Why was the SqlDataReader object created with the CloseConnection behavior in GetAllDoctors?

The connection must be open when you access the SqlDataReader object, so you must close the connection when you have finished using this object. The GetAllDoctors method returns the reader object so this means that you cannot close the connection in this method. Instead, the CloseConnection behavior means that the SqlDataReader object closes the connection when the reader object is closed, which will happen in the method that calls the GetAllDoctors method.

Common Issues Related to Accessing Databases by Using ADO.NET The following table lists some of the common problems that may occur when you use ADO.NET to access databases. For reasons why these errors occur, you must refer to relevant lessons in the module.

Issue Troubleshooting tip

Connection errors Check that the connection string is correct. You might have a spelling mistake. Consider using the DbConnectionStringBuilder for your data provider.

Application memory usage problems Check to see if you are closing connections and data readers after you have finished using them. Consider using Max Pool Size.

Problems retrieving data Check the command strings you are using, they may have spelling mistakes. Test query strings by using a tool such as sqlcmd. If a query has parameters consider using a stored procedure.

Best Practices for Accessing Databases by Using ADO.NET Supplement or modify the following best practices for your own work situations:

• Always open connections as late as possible and close them as early as possible. Design your code to use this principle. Use the Using construct or Finally clause to help you.

• Use the CloseConnection behavior if your function returns a DbDataReader.

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• Always close a DbDataReader as soon as possible: the Using construct and Finally clause help you here.

• Consider writing your code so that it is data provider independent by using DbProviderFactory and related classes. This means that if you choose to change your data source, the changes required in you code will be minimal.

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ITED Modifying Data by Using ADO.NET Commands 2-1

Module 2 Modifying Data by Using ADO.NET Commands

Contents: Lesson 1: Inserting, Updating and Deleting Data 2-3

Lesson 2: Managing Data Integrity and Concurrency 2-8

Lab: Modifying Data by Using ADO.NET Commands 2-14

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Module Overview

Many applications perform operations to query and update data in a database. Often an application must perform several such operations as a single unit of work, so that either all of the operations complete, or none complete. This unit of work is called a transaction. ADO.NET provides command classes and transaction classes that enable you to perform these tasks. This module will introduce the commands to modify the database and the classes used to perform transactions.

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Lesson 1 Inserting, Updating, and Deleting Data

This lesson describes the classes in ADO.NET that enable you to change the data in a database, and how to handle errors that might be returned from the database.

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Creating and Executing Commands to Modify Data

Key Points A command to modify data does not return a rowset; the only data that is returned is the number of rows affected by the command. To execute the operation, you create an ADO.NET command object, initialize the object with the command, and then execute it by invoking the ExecuteNonQuery method.

Question: Why would you invoke the ExecuteNonQuery method instead of invoking the ExecuteReader or ExecuteScalar method?

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Handling Exceptions When Modifying Data

Key Points Your command might perform an action on the database that is invalid. The server returns an error as a SqlException exception that you can catch in your code. The Errors collection contains details about the errors.

Question: When is an InvalidOperationException exception object thrown?

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Executing Long-Running Modifications Asynchronously

Key Points If a command is likely to take a long time to perform, you should not execute the command on the main thread of a graphical application because this blocks all of the processing of Windows messages. Such commands should be performed on a separate thread as an asynchronous command.

Question: What visible effects are you likely to see if the main thread of a graphical application is blocked by the performance of a lengthy operation?

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Demonstration: Inserting, Updating and Deleting Data

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Lesson 2 Managing Data Integrity and Concurrency

Transactions are an important part of data access because they ensure data integrity. However, by their nature, transactions restrict access to data, and so Microsoft® SQL Server® 2005 has settings that enable you to relax these restrictions according to the type of access operation that you want to perform.

This lesson will explain how to create and use transactions effectively.

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Overview of Transactions

Key Points The Atomicity, Consistency, Isolation, Durability (ACID) properties are the classic description of the properties that all transactions should have: atomic, consistent, isolated, and durable.

Question: What would happen if transactions are not used when transferring money from one bank account to another, and an error occurs before the second account is credited?

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Transactions and Concurrency

Key Points In a multi-user system more than one user may try to update a row. The concurrency model determines whether multiple users have concurrent access to the same row.

Question: Can you identify tables that do not need concurrent access?

Question: Can you identify tables that should always allow concurrent access?

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SQL Server 2005 Isolation Levels

Key Points Transactions are isolated items of work. However, complete isolation can affect the performance of your application if it runs more than one transaction at the same time on the same table. The isolation level allows you to relax isolation and enables you to improve concurrency.

Question: Which of these isolation levels, which gives the most concurrent access, and which gives the most isolation?

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Best Practices for Implementing Transactions

Key Points Depending on the isolation level used, a transaction locks data at some point, which consumes server resources that are deemed to be expensive. To use transactions efficiently you should keep the transaction as short as possible. You can also choose an isolation level to improve concurrency.

Question: Why should you keep the lifetime of a transaction as short as possible?

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Demonstration: Managing Data Integrity and Concurrency

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Lab: Modifying Data by Using ADO.NET Commands

Exercise 1: Inserting, Updating, and Deleting Data in a Database

Scenario You are a developer for the Medical Clinic Management System for Contoso, Ltd. The Contoso Clinic Management System is a healthcare system for hospitals and clinics that run specialist practices. The clinics must organize a set of consultants and equipment to service patient needs. The system supports both the management of appointments and the management of patient information.

In this Lab you will develop the code to manage patient data in the database. You will write code to access patient data, insert new patient, update, and delete existing patient records.



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2. Access patient data.

3. Insert a patient record.

4. Update a patient record.

5. Delete a patient record.


DEV-02.


Task 2: Access patient data 1. Open the ContosoMedical project:

• If you are using Microsoft Visual Basic® development system, go to E:\Labfiles\Starter\VB\ContosoMedical.

• If you are using Microsoft Visual C#® development tool, go to E:\Labfiles\Starter\CS\ContosoMedical.

2. In Solution Explorer, open the ContosoMedicalDatabases node, and then open the ContosoMedicalDB.dbo.Patients.SQL script.

3. Familiarize yourself with the schema of the table created by this script.

4. All of the data in the Patients table are added and modified by using stored procedures. Familiarize yourself with the stored procedures in this project.

5. Open the ClinicAdminClient form, click on the Patients tab and familiarize yourself with the following controls on this form:

• There are buttons to retrieve a patient and to create a new patient.

• There are controls to provide information like the first name, last name, gender and date of birth.

• There are buttons to insert, update, and delete database items according to the data in the controls.

• There is a picture box and a button to enable you to upload a picture.

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6. Implement the code for the Click event of the Get Patient button. This code retrieves the information for a patient by using the Patient ID and uses this data to update the controls on the form. To implement this method, paste the contents of the Ex1_Task2_getPatient_Click.txt file.

• Go to the folder E:\Labfiles\Starter\VB (Visual Basic).

• Go to the folder E:\Labfiles\Starter\CS (Visual C#).

7. In Microsoft Visual Studio® 2008, open the Data Access Component source file in the ContosoMedicalUtilities project. Open the source file is named:

• ContosoMedicalDAC.vb (Visual Basic).

• ContosoMedicalDAC.cs (Visual C#).

8. Implement the GetPatient method. The code for this method is in the Ex1_Task2_GetPatient.txt file. This code performs the following steps:

• Opens a database connection.

• Creates a command to execute the uspGetPatient stored procedure.

• The stored procedure has an in parameter so the code initializes the parameter on the command object.

• Calls the ExecuteReader to obtain a SqlDataReader object for the command.

• Reads the first and only row in the SqlDataReader object and uses the data to initialize the Patient object that is returned from the function.

9. Build and run the application. When the application starts:

• Click the Patients tab.

• In the Patient ID box, type 1

• Click Get Patient.

10. Verify that the following values are returned.

Control Value

First name Isabella

Last name Young

Gender The Female radio button is selected

DoB 31 December 1964

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11. Close the application.

Task 3: Insert a patient record 1. In the ContosoMedicalUtilities project node, open Patient.vb (Visual Basic)

or Patient.cs (Visual C#) file and familiarize yourself with this class.

2. In the ClinicAdminClient project, use the contents of the Ex1_Task3_insertPatient_Click.txt file to implement the Insert button Click handler. This code carries out these steps:

• Creates a new Patient object from the values in the controls on the form.

• Creates an instance of the data access component class and calls the InsertPatient method to write the data to the database and obtain the PatientID for the new patient.

• Write the PatientID value into the Patient ID text box.

3. Open the Data Access Component source file and locate the starter implementation for the InsertPatient method. Paste the contents of the Ex1_Task3_InsertPatient.txt file as the implementation of this method. The code performs these steps:


• Creates a command to call the uspInsertPatient stored procedure.

4. Add the following code to add the four input parameters of the command object that invokes the uspInsertPatient stored procedure:

Parameter Implement With

@firstName patient.FirstName

@lastName patient.LastName

@gender patient.Gender

@dateOfBirth patient.DateOfBirth

5. Add code to add an output parameter named @patientID to the command for

the stored procedure.

6. Write code to get the PatientID from the @patientID parameter.

7. Build the project and confirm that there are no compiler errors.

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8. Run the project and on the Patients tab insert a new patient. Make a note of the returned Patient ID because you will use it in the following tasks.

9. Close the application.

Task 4: Update a patient record 1. In the ClinicAdminClient project, use the contents of the

Ex1_Task4_updatePatient_Click.txt file to implement the Update button Click handler. The code performs these steps:

• Creates a new Patient object from the values in the controls on the form.

• Creates an instance of the data access component class and calls the UpdatePatient method to write the data to the database and obtain the PatientID for the new patient.

• Write the PatientID value into the Patient ID text box.

2. In the Data Access Component source file the starter implementation for the UpdatePatient method is provided in the Ex1_Task4_UpdatePatient.txt file. This code performs these steps:


• Creates a command to call the uspUpdatePatient stored procedure.

• Initializes the following parameters:

Parameter Implement With

@patientID patient.PatientID

@firstName patient.FirstName

@lastName patient.LastName

@gender patient.Gender

@dateOfBirth patient.DateOfBirth

• Executes the command.


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4. Run the application and, on the Patients tab, retrieve the patient that you added in the last task. Use the number you obtained in the last task in the Patient ID control.

5. Alter the patient data and then click Update.

6. Verify that the patient data is updated in the database.

Task 5: Delete a patient record 1. In the ClinicAdminClient project, use the contents of the

Ex1_Task5_deletePatient_Click.txt file to implement the Delete button Click handler. The code performs these steps:

• Creates a data access component and calls the DeletePatient method.

• If the patient is deleted from the database, clears the controls on the form.

2. Use the contents of the Ex1_Task5_DeletePatient.txt file to mplement the

DeletePatient method in the Data Access Component.

• Open a database connection.

• Create a command to call the uspUpdatePatient stored procedure.

• Initialize the @patientID parameter of the uspUpdatePatient stored procedure with patient.PatientID.

• Execute the command.

• If the patient is deleted from the database, call the uspArchivePatient stored procedure to add information about the deleted data to the database.


4. Run the application and, on the Patients tab, delete the patient that you added in the last task. Use the number you obtained in the last task in the Patient ID control.

5. Verify that the patient is deleted in the database.

Results: After this exercise, you should have written code that retrieves, inserts, changes, and deletes patient data in the database.

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Exercise 2: Implementing Transactional Updates

Scenario The DeletePatient method that you implemented in the last exercise deletes patient information from the Patients table and archives information about this patient in the ArchivedPatients table. This is an operation that should be carried out under a transaction because if it is not possible to archive the data in the ArchivedPatients table, the data should not be removed from the Patients table. In this exercise you will change the DeletePatient method to use a transaction and test this code by using a special value for the patient name that will cause uspArchivePatient to fail.


1. Examine the ArchivedPatients table.

2. Add transactional behavior to the DeletePatient method.

3. Verify that the transaction commits if all of the operations succeed..

4. Verify that the transaction rolls back if an error occurs.

Task 1: Examine the ArchivedPatients table 1. In the ContosoMedicalDatabases project, open the

ContosoMedicalDB.dbo.ArchivedPatients.SQL script. Familiarize yourself with the ArchivedPatients table.

2. Open the ContosoMedicalDB.dbo.uspArchivePatient.SQL script and familiarize yourself with the uspArchivePatient stored procedure.

• This procedure checks whether the @fullName parameter is the value of Dummy Patient and, if so, it raises an error.

Task 2: Add transactional behavior to the DeletePatient method 1. In Solution Explorer, in the ContosoMedicalUtilities project, double-click

ContosoMedicalDAC.vb (Visual Basic) or ContosoMedicalDAC.cs (Visual C#). Add transaction support to the command objects in the DeletePatient method.

• Declare a transaction reference at the top of the method:

[Visual Basic]

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Dim transaction As SqlTransaction = Nothing

[Visual C#] SqlTransaction transaction = null;

• After the connection is opened, initialize the transaction object by calling BeginTransaction on the connection object.

• Use this transaction object to initialize the command object. Provide the transaction object as an additional parameter to the constructor of this SqlCommand object:

[Visual Basic] Dim command As New SqlCommand( _ "uspDeletePatient", connection, transaction)

[Visual C#] SqlCommand command = new SqlCommand( "uspDeletePatient", connection, transaction);

• Do the same thing for the archiveCommand command object.

2. After the archiveCommand is executed, commit the transaction if the

command is successful, and rollback the transaction if the command failed.

3. Add an exception handler to rollback the transaction if any exceptions are thrown in the code.

Task 3: Verify that the transaction commits if all of the operations succeed 1. Build the solution and confirm that there are no compiler errors.

2. Run the application and on the Patients tab add a new patient.

3. Delete the patient that you just added.

4. Test to see if the patient data was deleted by trying to retrieve the patient. Confirm that when you click Get Patient, a dialog indicates that the patient ID is not recognized, which confirms that the record has been deleted successfully.

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Task 4: Verify that the transaction rolls back if an error occurs 1. Run the application again.

2. On the Patients tab, add a new patient. Use the following values and make sure that you use the exact spelling and capitalization as given here (ignore the other controls). Make a note of the Patient ID.

Control Value

First name Dummy

Last name Patient

3. Delete the patient that you just inserted. Verify that the Cannot archive

Dummy Patient dialog is shown.

4. Confirm that the patient data was not deleted by retrieving the data again from the database by clicking Get Patient.

Results: After this exercise, you should have implemented transactional semantics for the Delete button, so that either items are deleted and archived as one operation, or do not happen at all.

Exercise 3: Executing Commands Asynchronously

Scenario Operations that involve passing large amounts of data over the network take time and so, such operations must not be performed on the user interface thread. In this exercise you will perform a data operation that will take a long time: inserting and accessing bitmap images into the database. To prevent the operation affecting the user interface, you will implement the code to read and write bitmaps as asynchronous operations.


1. Add the Asyncronous Processing flag to the configuration file.

2. Implement the code to asynchronously upload a photograph for a patient.

3. Build and test the code.

4. Implement the code to asynchronously get a photograph for a patient.

5. Build and test the code.

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Task 1: Add the Asynchronous Processing flag to the configuration file 1. In the ClinicAdminClient project, open the App.config file in the code editor.

2. Add the following code to the end of the connectionString value, and make sure that there is a semicolon between the end of the existing string and the beginning of the new string.

Asynchronous Processing=true

3. Save this file.

Task 2: Implement the code to asynchronously upload a photograph for a patient 1. Open the code for the ClinicAdminForm form and locate the Click handler

for the Upload New Photo button.

2. Paste the contents of the Ex3_Task2_uploadNewPhoto.txt file as the implementation of this method.

• Go to folder E:\Labfiles\Starter\VB\Ex3 (Visual Basic).

• Go to folder E:\Labfiles\Starter\CS\Ex3 (Visual C#).

The uploadNewPhoto_Click method calls BeginSavePhoto on the Data Access Component (which you will implement in a moment). The BeginSavePhoto method is provided with a callback to the SavePhotoCallback method.

3. The SavePhotoCallback method is provided in the Ex3_Task2_SavePhotoCallback.txt file. Paste the contents of this method after the uploadNewPhoto_Click method. This method retrieves the result of the command and then calls the SavePhotoUI on the user interface thread by using the SavePhotoUIDelegate delegate.

4. Use the contents of the Ex3_Task4_BeginSavePhoto.txt file to implement the BeginSavePhoto method in the Data Access Component. This method calls the uspSavePatientPhoto stored procedure asynchronously.

Task 3: Build and test the code 1. Build the solution and confirm that there are no compiler errors.

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2. Run the application.

3. On the Patients tab, open the first patient by typing 1 in the Patient ID control and clicking Get Patient.

4. Click Upload New Photo, and in the Open File dialog box, select female.jpg in the E:\Labfiles\Starter folder.

5. In the Open File dialog box, click OK to see the photograph, which will appear immediately on the form, and three seconds later you will see the Photo saved successfully dialog box which indicates that the operation to write the data into the database completed.

Task 4: Implement the code to asynchronously get a photograph for a patient 1. Open the code for the ClinicAdminForm form and locate the Click handler

for the Get Patient button.

2. After the method has initialized the form controls with the results from calling the GetPatient method on the Data Access Component, add the following line to read the photograph from the database, and use this code to initialize the photograph control on the form.

[Visual Basic] GetPhoto(Int32.Parse(patientID))

[Visual C#] GetPhoto(int.Parse(patientID));

3. Paste the contents of the Ex3_Task4_GetPhoto.txt file after the getPatient_Click method. This file has the GetPhoto method and supporting methods.

4. GetPhoto calls BeginGetPhoto on the Data Access Component. Implement this code with the contents of the Ex3_Task4_BeginGetPhoto.txt file.

5. Review the code that you have just pasted.

• GetPhoto calls BeginGetPhoto on the Data Access Component by passing a delegate to GetPhotoCallback.

• BeginGetPhoto executes uspGetPatientPhoto asynchronously.

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• When the stored procedure completes, the GetPhotoCallback method is called and harvests the results of the call. This method uses the data to update the user interface, which is has to do on the user interface thread, and so it calls BeginInvoke by passing a delegate to GetPhotoUI.

• The GetPhotoUI method accesses the SqlDataReader object created as a result of the command, reads the binary data, and uses the data to update the photograph control.

Task 5: Build and test the code 1. Build the solution and confirm that there are no compiler errors.

2. Run the application and click the Patients tab.

3. Load the first patient: in the Patient ID text box type 1 and then click Get Patient.

4. The controls are updated immediately and show the values for the first patient. After three seconds the photograph appears.

Results: After this exercise, you should have implemented asynchronous reads and writes of data to the database. You should also have handled all user interface updates on the user interface thread.

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Review Questions 1. In the lab, why did you use BeginInvoke in the callback method?

The callback method is called on the thread that executes the command asynchronously. This is not the user interface thread. The user interface can only be changed by the user interface thread and you do this by calling BeginInvoke by passing a delegate to the method that updates the user interface.

2. Why would you relax the isolation level of a transaction?

If you use the most isolated level, rows used by the transaction are locked until the transaction completes. This has the effect of serializing operations so that they perform one after each other and, for a multi-user system, this affects the overall performance of the system. If you relax the isolation level then you can increase concurrency and prevent the blocking of users.

3. Why make transactions isolated at all?

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If your application writes data to rows in the database, you must restrict some concurrency to make sure that the data that one user reads truly reflects the data in the row. Only by careful analysis of the application can you determine the concurrency model that is best for your application.

Best Practices Supplement or modify the following best practices for your own work situations:

• Use transactions to make two or more operations atomic.

• Use the transaction isolation level to control concurrency.

• Keep the transaction time as short as possible.

• Integrate transaction rollback as part of your error handling.

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ITED Querying and Maintaining Data by Using DataSets 3-1

Module 3 Querying and Maintaining Data by Using DataSets

Contents: Lesson 1: Creating and Using a DataSet to Retrieve Data 3-3

Lesson 2: Updating a Database by Using a DataSet 3-10

Lesson 3: Using a DataSet in an Occasionally Connected Environment 3-16

Lab: Querying and Maintaining Data by Using DataSets 3-19

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Module Overview

ADO.NET provides extensive support for creating disconnected applications, if the application is not directly connected to a server for a source of data or for a middle-tier service. Mobile users who work with notebook computers are the primary users in disconnected applications.

The primary class in disconnected applications is the DataSet class. A DataSet is an in-memory cache of tables, typically populated from a database.

This module describes how to create a DataSet object, fill it with data, work with the data while disconnected from the database, and then reconnect to the database when you are ready to save the DataSet data.

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Lesson 1 Creating and Using a DataSet to Retrieve Data

ADO.NET is a collection of classes that connect to a database, perform actions on the database, and retrieve data from the database. A collection of such classes is known as a data provider and is used to access data from a specific data source. In addition to the fundamental classes for accessing data through a data source, the Microsoft® .NET Framework also provides language features and class libraries that use ADO.NET to further abstract data access.

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Overview of DataSets

Key Points A DataSet object is an in-memory cache of data that is typically retrieved from a database.

A DataSet can contain any number of DataTable objects. Each DataTable contains a collection of columns that define the schema of the table, and a collection of rows that contain the data for the table.

You can define relations and constraints between the DataTable objects in a DataSet, to represent the corresponding relationships between tables in the database.

Question: What tables and relations might you define for DataSet objects in your own applications?

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Untyped and Typed DataSets

Key Points The System.Data.DataSet class is an untyped DataSet class. To access tables and columns in an untyped DataSet, you must specify the index or string literal name of the table or column. If you specify an invalid index or string literal name, a run time exception occurs.

A typed DataSet is a class that you generate by using Micosoft Visual Studio® wizards, and contains nested properties and classes that provide type-safe access to the tables and columns. If you specify an invalid table name or column name, you obtain a compile time error instead of a run time exception.

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Creating an Untyped DataSet

Key Points ADO.NET 3.5 is a collection of classes that is part of the .NET Framework library. In addition, Visual Studio® has designers that generate ADO.NET code for you.

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Demonstration: Defining a Typed DataSet Class

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Retrieving Data into a DataSet

Key Points When you create a typed DataSet class, Visual Studio generates TableAdapter classes that provide Fill methods to fill each table in the DataSet.

If you are using an untyped DataSet, you can fill the DataSet by using a DataAdapter class such as SqlDataAdapter. To specify the SQL query that will retrieve data from the database, you must set the SelectCommand property on the DataAdapter object. You can then invoke the Fill method on the DataAdapter object, which executes the SQL query and fills a table in the DataSet.

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Accessing Data in a DataSet

Key Points To access rows in a typed DataSet table, you use the Rows property to get a collection of rows, and then access columns in each row by using type-safe properties. Alternatively, you can create a DataTableReader object on a typed or untyped DataSet table, and then access columns by index or column name.

To find a specific row in a typed DataSet table, you invoke the FindByXxx method on the table. The precise name of the method is generated by Visual Studio according to the name of the primary key column in the DataSet table.

To select all of the rows in a typed or untyped DataSet table that match a specified filter expression, you invoke the Select method on the table. The method returns an array of untyped DataRow objects that match the specified filter expression.

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Lesson 2 Updating a Database by Using a DataSet

This lesson shows how to modify data in a DataSet, validate the modifications, and then save the modified data back to the database. The lesson also describes how to resolve optimistic concurrency conflicts, which can occur if two or more users or processes attempt to make conflicting changes to data in the database.

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Modifying Data in a DataSet

Key Points To add a row to a typed DataSet table, you invoke the AddXxxRow method on the table. Another way to add a row to a typed or untyped DataSet table is to invoke the Add or InsertAt method on the DataTable Rows property.

To permanently remove a row from a typed DataSet table, you invoke the RemoveXxxRow method on the table. Another way to permanently remove a row from a typed or untyped DataSet table is to invoke the Remove or RemoveAt method on the DataTable Rows property.

To mark a row to be deleted from a typed or untyped DataSet table, you invoke the Delete method on a DataRow object.

You can access the original value of data in a DataRow by specifying the DataRowVersion.Original enumeration value when you access a column.

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Validating Modified Data in a DataSet

Key Points If you attempt to save a DataSet that contains erroneous rows, a run time exception occurs. To avoid the exception, you should first determine whether the DataSet contains any erroneous data, and then reject the erroneous rows before you save the DataSet

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Saving Modified Data to a Database

Key Points When you create a typed DataSet class, the associated TableAdapter classes provide Update methods to save each table in the DataSet to the database.

If you are using an untyped DataSet, you can fill the DataSet by using a DataAdapter class such as SqlDataAdapter. You must set the InsertCommand, UpdateCommand, and DeleteCommand properties on the DataAdapter object, to specify the SQL statement that you want to insert, update, or delete a row in the database. You can then invoke the Update method on the DataAdapter object, to execute the appropriate SQL statements to save the table modifications to the database.

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Resolving Optimistic Concurrency Conflicts

Key Points Optimistic concurrency conflicts occur when you save a DataSet to the database, but the rows in the database have already been modified. ADO.NET DataSets enable you to detect optimistic concurrency conflicts and to handle them in one of the following ways:

• Force the current row to be saved and to overwrite the existing data in the database.

• Skip the current row and continue saving subsequent rows.

• Skip all of the subsequent rows.

Question: When might you use each optimistic concurrency strategy in your own applications?

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Demonstration: Updating a Database by Using a DataSet

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Lesson 3 Using a DataSet in an Occasionally Connected Environment

The ADO.NET DataSet class is designed to be used in occasionally connected environments if an application has intermittent access to the database. This lesson describes how you can store DataSet data locally in XML format while the database is unavailable, and then repopulate the DataSet from XML data later.

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Using a DataSet as a Cache in an Occasionally Connected Environment

Key Points You can serialize the data in a DataSet object to an XML document. This is useful if you want to preserve the data between application invocations. The next time the application starts, you can repopulate the DataSet object from the XML document.

The ability to serialize a DataSet as XML is also useful in distributed applications, if you want to transmit a DataSet over a network to a remote client.

To serialize a DataSet object as XML data, you invoke the WriteXml method on the DataSet object. To fill a DataSet object by using XML data, you invoke the ReadXml method on the DataSet object.

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Serializing and Deserializing a DataSet as XML

Key Points When you serialize and deserialize XML data for a DataSet object, you specify the DiffGram format to preserve information about the data modifications in the DataSet.

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Lab: Using a DataSet to Retrieve and Modify Data

Exercise 1: Creating a Typed DataSet

Scenario You are a developer for the Medical Clinic Management System for Contoso, Ltd. The Contoso Clinic Management System is a healthcare system for hospitals and clinics that run specialist practices. The clinic must organize a set of consultants and equipment to service patient needs.

In this exercise, you will create a typed DataSet to represent the following tables in the Contoso Medical database.

Table Description

Doctors Contains information about all of the doctors who are employed by the Contoso Medical Clinic.

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Table Description

Patients Contains information about all of the patients registered at the Contoso Medical Clinic.

Appointments Contains appointment information. The Appointments table has foreign keys named DoctorID and PatientID, which identify the doctor and the patient for the appointment.

The table also has a column named AppointmentDateTime that identifies the date and time of the appointment, and a column named Notes that contains notes entered by the doctor after the appointment has taken place.

You will also define relations and constraints between the Doctors and Appointments tables, and between the Patients and Appointments tables.

You will use the typed DataSet in a Windows Forms application named AppointmentViewer, which enables a doctor to view appointments and to modify notes for an appointment.

Note: The database server name for this lab is .\SQLEXPRESS and the database name is ContosoMedicalDB.



2. Create a typed DataSet.

3. Add tables to the typed DataSet.

4. Add relations and constraints to the typed DataSet.

5. Review the typed DataSet class definition.


DEV-03.


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Task 2: Create a typed DataSet 1. Open Microsoft Visual Studio 2008.

2. If you are using Visual Basic, open the solution E:\Labfiles\Starter\VB\ContosoMedical\ContosoMedical.sln. If you are using Visual C#, open the solution E:\Labfiles\Starter\CS\ContosoMedical\ContosoMedical.sln.

3. In the AppointmentViewer project, add a new DataSet named ContosoMedicalDataSet.xsd.

Task 3: Add tables to the typed DataSet 1. Add a table named Doctors to the ContosoMedicalDataSet.xsd DataSet, that

contains the ID and the full name of the doctor. Specify the following SQL statement to query the doctor details, but do not generate commands to insert, update, or delete doctors.

select DoctorID, FullName=FirstName + ' ' + LastName from Doctors

Verify that the DataSet designer displays a table named Doctors and an associated table adapter named DoctorsTableAdapter.

2. Add a table named Patients to the ContosoMedicalDataSet.xsd DataSet, that contains the ID, full name, gender, and date of birth of the patient. Specify the following SQL statement to query the patient details, but do not generate commands to insert, update, or delete patients.

select PatientID, FullName=FirstName + ' ' + LastName, Gender, DateOfBirth from Patients

Verify that the DataSet designer now displays a table named Patients and an associated table adapter named PatientsTableAdapter.

3. Add a table named Appointments to the ContosoMedicalDataSet.xsd DataSet, that contains all of the appointment details.

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When prompted, specify that you want Visual Studio to create new stored procedures to select, insert, update, and delete appointments. Provide the following SQL statement for the SELECT stored procedure.

select * from Appointments

Specify the following names for the stored procedures:

• Select: uspGetAppointments

• Insert: uspInsertAppointment

• Update: uspUpdateAppointment

• Delete: uspDeleteAppointment

Preview the SQL script that Visual Studio will use to generate the stored procedures. Verify that the uspUpdateAppointment and uspDeleteAppointment stored procedures perform optimistic concurrency tests that prevent the row from being updated or deleted if it has already been modified in the database.

When you have completed these steps, verify that the DataSet designer now displays a table named Appointments, with an associated table adapter named AppointmentsTableAdapter.

4. Save ContosoMedicalDataSet.xsd.

Task 4: Add relations and constraints to the typed DataSet 1. Add a relation and foreign key constraint between the Doctors and

Appointments tables in the ContosoMedicalDataSet.xsd DataSet, which represents the relationship between the DoctorID primary key in the Doctors database table and the DoctorID foreign key in the Appointments database table.

2. Add a relation and foreign key constraint between the Patients and Appointments tables in the ContosoMedicalDataSet.xsd DataSet, which represents the relationship between the PatientID primary key in the Patients database table and the PatientID foreign key in the Appointments database table.

3. Save ContosoMedicalDataSet.xsd.

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Task 5: Review the typed DataSet class definition 1. In the AppointmentViewer project, open

ContosoMedicalDataSet.Designer.vb (Visual Basic) or ContosoMedicalDataSet.Designer.cs (Visual C#) in the editor.

2. Verify that the source file defines a ContosoMedicalDataSet class that contains the following strongly typed data table classes:

• DoctorsDataTable

• PatientsDataTable

• AppointmentsDataTable

3. Verify that the source file defines a namespace named AppointmentViewer.ContosoMedicalDataSetTableAdapters that contains the following strongly typed table adapter classes:

• DoctorsTableAdapter

• PatientsTableAdapter

• AppointmentsTableAdapter

Note: In Visual Basic, the source code specifies the namespace name as ContosoMedicalDataSetTableAdapters. This namespace is implicitly nested in the root namespace for the project, AppointmentViewer.

Results: After this exercise, you should have created a typed DataSet that contains tables named Doctors, Patients, and Appointments. You should also have defined relations and constraints between the Doctors and Appointments tables, and between the Patients and Appointments tables.

Exercise 2: Retrieving Data into a DataSet In this exercise, you will add code to the main form in the ApplicationViewer application, to create a DataSet instance and to populate it from either the database or a local XML file.

You will also add code to display a list of all of the doctors in a DataGridView control, and to display a list of appointments for a particular doctor and date in another DataGridView control.


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1. Review the main form in the AppointmentViewer application.

2. Create a DataSet instance.

3. Populate the DataSet instance.

4. Display all of the doctors.

5. Display appointments for a particular doctor and date.

Task 1: Review the main form in the AppointmentViewer application 1. Open MainForm.vb (Visual Basic) or MainForm.cs (Visual C#) in the form

designer.

2. Review the following features in the form:

• The upper DataGridView control, doctorsGridView, will display all of the doctors in the DataSet Doctors table.

• The lower DataGridView control, appointmentsGridView, will display the appointments for the currently selected doctor and date.

Task 2: Create a typed DataSet instance 1. View the code for MainForm.vb (Visual Basic) or MainForm.cs (Visual C#).

2. Locate the comment TODO: Import the namespace that contains the TableAdapter classes, and add code to import the AppointmentViewer.ContosoMedicalDataSetTableAdapters namespace.

3. Locate the comment TODO: Create a typed DataSet instance, and add code to create a ContosoMedicalDataSet instance named _dataset.

Task 3: Populate the DataSet instance 1. In the MainForm class, locate the InitDataSetFromLocalFile method.

If a local XML file exists, the application invokes this method during initialization to fill the DataSet by using the data in the XML file. The XML file stores the DataSet data in DiffGram format.

2. Where indicated by the comment TODO: Fill the DataSet from a local XML file, add code to fill _dataset from the XML file specified by _xmlFileName.

3. Locate the InitDataSetFromDatabase method.

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If the local XML file does not exist, the application invokes this method during initialization to fill the DataSet from the database.

4. Where indicated by the comments in the InitDataSetFromDatabase method, add code to fill the Doctors, Patients, and Appointments tables in the DataSet by using a DoctorsTableAdapter, PatientsTableAdapter, and AppointmentsTableAdapter respectively.

Task 4: Display all of the doctors 1. In the MainForm class, locate the MainForm_Load method.

2. Where indicated by the comment TODO: Display all doctors, add code to iterate through all of the rows in the DataSet Doctors table, and add each doctor to the doctorsGridView control.

Tip: To add a row to the grid view, invoke the doctorsGridView.Rows.Add method. Pass two parameters into the method, to display the DoctorID and FullName properties for the doctor.

3. Build and run the application.

Verify that the Appointment Viewer window displays a list of doctors in the upper DataGridView control.

4. Close the Appointment Viewer window and return to Visual Studio.

Task 5: Display appointments for a particular doctor and date 1. In the MainForm class, locate the DisplayAppointments method.

The application invokes this method when the user changes the currently selected doctor or date on the form.

2. Review the code at the start of the method, which performs the following tasks:

a. Clears the contents of the appointmentsGridView control.

b. Gets the doctor ID and the appointment data specified by the user.

c. Creates a filer expression to select appointments for the specified doctor and date.

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3. Where indicated by the comment TODO: Select rows from the DataSet Appointments table, add code to select rows from the DataSet Appointments table by using the filter filter expression.

4. Where indicated by the comment TODO: Display each appointment in appointmentsGridView, add code to display each appointment as follows:

a. Iterate through the appointment rows that you obtained in step 3.

b. Get the AppointmentID, PatientID, and AppointmentDateTime columns for the appointment row.

c. Get the row in the Patients table that corresponds to the appointment.

d. Add an item to the appointmentsGridView control, to display the appointment ID, patient ID, appointment time (as a short time), patient name, patient gender, and patient date of birth (as a short date.)

Note: The appointment ID and patient ID columns are not visible in the appointmentsGridView control. These columns are included to identify the appointment and patient for other code in the application, which you will write shortly.


Verify that the Appointment Viewer window displays a list of doctors in the upper DataGridView control.

6. Select the following details in the Appointment Viewer window:

• Doctor: Ian Jenkins

• Date: Monday, June 02, 2008

Verify that the application displays the following appointments for the selected doctor and date:

11:00 AM, Isabella Young, F, 12/31/1964 11:30 AM, Justin Harris, M, 2/1/1966 12:00 PM, Jenna Parker, F, 12/5/1974 12:30 PM, Heidi Chandra, F, 1/19/1985

Select the following details in the Appointment Viewer window:


• Date: Tuesday, June 03, 2008

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11:00 AM, Olivia Torres, F, 9/27/1974 11:30 AM, Gabriel Chow, M, 12/3/1991 12:00 PM, Fernando King, M, 1/2/1980

Select the following details in the Appointment Viewer window:

• Doctor: Chloe Young

• Date: Tuesday, June 03, 2008


11:00 AM, Derrick Alonso, M, 6/7/1984 2:00 PM, Meghan Gutierrez, F, 9/8/1978

7. Close the Appointment Viewer window and return to Visual Studio.

Results: After this exercise, you should have created a DataSet instance, populated it from a database or from a local XML file, and displayed the data in a form.

Exercise 3: Modifying Data in a DataSet In this exercise, you will enable the user to edit appointment notes. The Appointments table in the database contains a Notes column to hold this value persistently, and the Appointments table in the DataSet contains a similar column to hold this value temporarily in memory.

When the user double-clicks an appointment in the AppointmentViewer application, the application will display the appointment notes in a new window. The user can modify the notes for an appointment if appropriate, and then close the window. When the user closes the window, the application will store the updated appointment notes in the DataSet.


1. Review the form to edit appointment notes in the AppointmentViewer application.

2. Modify appointment notes in the DataSet.

3. Build and test the application.

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Task 1: Review the form to edit appointment notes in the AppointmentViewer application 1. Open EditNotesForm.vb (Visual Basic) or EditNotesForm.cs in the form

designer.

2. Verify that the form contains a text box named notesTextBox that enables the user to view and edit the notes for a particular appointment.

3. View the code for the EditNotesForm class.

4. Verify that the EditNotesForm class has a property named Notes that gets and sets the text value in the notesTextBox control.

Task 2: Modify appointment notes in the DataSet 1. View the code for MainForm.vb (Visual Basic) or MainForm.cs (Visual C#).

2. Locate the appointmentsGridView_DoubleClick method.

The application invokes this method when the user double-clicks an appointment in the appointmentsGridView control.

3. Where indicated by the comment TODO: Lookup the appointment row in the DataSet Appointments table, add code to get the row in the Appointments table for the specified appointmentID value.

4. Where indicated by the comment TODO: Set the Notes property on the form, add code to set the Notes property on the EditNotesForm instance to display the notes for the current appointment in the DataSet.

5. Where indicated by the comment TODO: Store the appointment notes in the appointment row, add code to retrieve the Notes value from the form and assign it to the Notes property for the appointment in the DataSet.

Task 3: Build and test the application 1. Build and run the application.




3. In the lower DataGridView control, double-click the first appointment.

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Verify that the Appointment Notes window displays No notes.

4. Type new notes into the text box, and then click OK to return to the Appointment Viewer window.

5. In the Appointment Viewer window, in the lower DataGridView control, double-click the first appointment again.

Verify that the Appointment Notes window displays the notes that you entered in the previous step.

6. Close the Appointment Notes window and the Appointment Viewer window, and return to Visual Studio.

Results: After this exercise, you should have modified the appointment notes in the Appointments table in the DataSet.

Exercise 4: Saving a DataSet and Resolving Conflicts In this exercise, you will add code to enable the user to save DataSet changes to a local XML file or to the database.

You will also add code to detect and resolve conflicts that might occur when saving the DataSet to the database. Such conflicts arise if two users attempt to edit and save appointment notes for the same appointment. When this happens, you will reject the changes made by the second user for that appointment, and then continue saving the remainder of the changes for the second user.


1. Pass the DataSet instance into a form to enable the user to save the DataSet.

2. Save the DataSet to a local XML file.

3. Save the DataSet to the database.

4. Verify that the application saves DataSet data.

5. Verify that the application detects and resolves optimistic concurrency conflicts.

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Task 1: Pass the DataSet instance into a form to enable the user to save the DataSet 1. Open CloseApplicationForm.vb (Visual Basic) or CloseApplicationForm.cs

(Visual C#) in the form designer.

2. Verify that the form contains four buttons. You will implement the following functionality for the buttons in the form:

Button Description of functionality

Save Locally Save the entire DataSet to a local XML file as a DiffGram, which retains information about the modifications made by the user.

Save to Database Save the Appointments table in the DataSet to the database.

Discard Changes Discard all of the modifications made to the DataSet since it was downloaded from the database.

Cancel Cancel the close-form operation.

3. View the code for the CloseApplicationForm class.

4. Locate the comment TODO: Import the namespace that contains the TableAdapter classes, and add code to import the AppointmentViewer.ContosoMedicalDataSetTableAdapters namespace.

5. Locate the comment TODO: Declare a typed DataSet variable, and add code to declare a ContosoMedicalDataSet instance named _dataset.

6. Locate the comment TODO: Retain a reference to the DataSet instance, and modify the constructor to receive a parameter to initialize the _dataset instance variable.

7. Open the code for MainForm.vb (Visual Basic) or MainForm.cs (Visual C#).

8. Locate the MainForm_FormClosing method.

The application invokes this method when the user closes the main form in the application.

9. Implement the MainForm_FormClosing method by adding the code in the Ex4_Task1.txt file, located in the folder E:\Labfiles\Starter\VB (Visual Basic) or E:\Labfiles\Starter\CS (Visual C#).

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Task 2: Save the DataSet to a local XML file 1. View the code for CloseApplicationForm.vb (Visual Basic) or

CloseApplicationForm.cs (Visual C#).

2. Locate the saveLocally_Click method, and add code to save the entire DataSet as an XML file in DiffGram format. Specify _xmlFileName as the name of the XML file.

Task 3: Save the DataSet to the database 1. Locate the saveToDatabase_Click method, and add code to save the DataSet

Appointments table to the database as follows:

a. Create an AppointmentsTableAdapter object.

b. Handle the RowUpdated event on the data adapter for the AppointmentsTableAdapter object. Specify Adapter_RowUpdated as the name of the event handler method.

c. Invoke the Update method on the AppointmentsTableAdapter object, to save the DataSet Appointments table to the database.

2. Implement the Adapter_RowUpdated event-handler method so that it detects and resolves optimistic concurrency conflicts, as follows:

a. Test the RecordsAffected property of the SqlRowUpdatedEventArgs parameter.

b. If RecordsAffected is zero, it indicates that the attempt to update a row in the DataSet Appointments table failed. In this case, display the appointment notes in a message box, and specify that the row should be skipped.

3. Locate the discardChanges_Click method, and add code to discard changes to the DataSet Appointments table.

Task 4: Verify that the application saves DataSet data 1. Build and run the application.




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3. In the lower DataGridView control, double-click the first appointment.

4. Type new notes into the text box, and then click OK to return to the Appointment Viewer window.

5. Close the Appointment Viewer window. In the Save Changes? dialog box, click Save Locally.

6. In Visual Studio, in Solution Explorer, expand the AppointmentViewer project, expand the bin folder, and then expand the Debug folder. Verify that the Debug folder contains a file named ContosoMedicalDataSet.xml, which contains the DataSet data that you just saved.

7. In Visual Studio, run the application again.




9. In the lower DataGridView control, double-click the first appointment. Verify that the Appointment Notes window displays the notes that you provided earlier. This confirms that the application has saved and restored the DataSet data to the local XML file successfully.

10. Close the Appointment Notes window and then close the Appointment Viewer window. In the Save Changes? dialog box, click Save to Database.

Task 5: Verify that the application detects and resolves optimistic concurrency conflicts 1. In Visual Studio, run the application again.

2. Modify appointment notes in the Appointment Viewer window, as follows:

• Select the doctor Ian Jenkins.

• Select the date Monday, June 02, 2008.

• Edit the notes for the first appointment.

Do not close the Appointment Viewer window yet.

3. Switch back to Visual Studio and start another instance of the Appointment Viewer application.

4. Modify appointment notes in the new Appointment Viewer window, as follows:

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• Edit the notes for all of the appointments.

5. Switch to the first Appointment Viewer window, and then close the window. In the Save Changes? window, click Save to Database.

Verify that the application closes without any errors, which indicates that the application saved the data to the database successfully.

6. Close the other Appointment Viewer window. In the Save Changes? window, click Save to Database.

Verify that the application displays a message box indicating that the application detected an optimistic concurrency error for the first appointment, because it has already been updated in the database. Verify that no other error messages appear, which indicates that the application saved the other appointments successfully.

7. In Visual Studio, start another instance of the Appointment Viewer application.

8. Verify that the application displays the correct appointment notes, as follows:



• Verify that the first appointment contains the notes that you supplied in the first Appointment Viewer window.

• Verify that the other appointments contain the notes that you supplied in the second Appointment Viewer window.

9. Close the Appointment Viewer window.

10. Close Visual Studio.

Results: After this exercise, you should have saved a DataSet to a local XML file or to the database. You should also have detected and resolved optimistic concurrency errors that might occur when a DataSet is saved to the database.

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Review Questions 1. What are the benefits of using typed DataSets rather than untyped DataSets?

A typed DataSet class contains properties that provide type-safe access to the tables in the DataSet. Each table is represented by a separated class that provides type-safe access to the columns in the table. Each table also has an associated TableAdapter class that contains pre-configured Fill and Update methods to populate and save the DataSet table.

2. How do you load data into a typed DataSet table from a database, and save the data back to the database later?

To load data into a typed DataSet table from a database, you create an instance of the appropriate TableAdater class and invoke the Fill method. To save the data back to the database, you invoke the Update method on the TableAdapter instance.

3. List four ways to access rows in a typed DataSet table.

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Iterate through the Rows collection in the table.

Create a DataTableReader object and use it to get each row in the table.

Get a particular row by its primary key value, by invoking the FindBy<PrimaryKey> method.

Get all of the rows that match a particular filter expression, by invoking the Select method.

4. What is the difference between deleting a row and removing a row in a DataSet table?

When you delete a row, you mark the row for deletion the next time the DataSet is saved to the database; the row is not physically removed until that time. When you remove a row, the row is physically removed immediately.

5. What is a DiffGram?

A DiffGram is an XML format that you can specify when you serialize a DataSet instance to XML, or when you populate a DataSet instance from XML. The DiffGram format preserves information about which rows have been added, modified, or deleted in the DataSet.

Common Issues related to Accessing Databases With ADO.NET The following table lists some of the common problems that occur when you query and maintain data by using DataSets.


Optimistic concurrency conflicts

Handle the RowUpdated event on the DataAdapter object. Implement a consistent strategy for handling optimistic concurrency conflicts, such as always rejecting row modifications that cause optimistic concurrency conflicts.

Automatic key generation If you add rows to a DataTable that contains automatically-generated column values, such as auto-increment primary keys, the values are not assigned until you save the DataSet to the database. Do not attempt to use these values in your application until you save the DataSet.

Saving dependent tables If a DataSet contains related tables, you might need to save the added rows, modified rows,

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and deleted rows separately for each table in the DataSet to preserve referential integrity in the database. Invoke the GetChanges method on a DataTable to get the subset of rows that have been added, modified, or deleted.

Best Practices for Querying and Maintaining Data by Using DataSets Supplement or modify the following best practices for your own work situations:

• Use typed DataSets where possible, because they provide better compile-time type safety and are easier to use than untyped DataSets.

• If you do not need to save DataSet modifications to the database, do not generate methods to insert, update, or delete rows in the DataSet.

• Define separate tables in the DataSet to match the tables in the database. Do not join multiple database tables into a single table in the DataSet, unless the schema is simple or you require read-only access to the data.

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ITED Querying and Maintaining Data by Using LINQ 4-1

Module 4 Querying and Maintaining Data by Using LINQ

Contents: Lesson 1: Querying In-Memory Data by Using LINQ Query Expressions 4-3

Lesson 2: Retrieving Data by Using LINQ to SQL 4-9

Lesson 3: Modifying Data by Using LINQ to SQL 4-16

Lab: Querying and Maintaining Data by Using LINQ to SQL 4-20

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Module Overview

Language-Integrated Query (LINQ) is a new technology that was introduced in the Microsoft® .NET Framework 3.5 and which enables you to query and maintain different types of data consistently. You can use LINQ to access data in a collection of objects, a database, a DataSet object, or an XML document by using a uniform set of keywords and application programming interface (API) calls.

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Lesson 1 Querying In-Memory Data by Using LINQ Query Expressions

This lesson describes how to define LINQ queries to access in-memory data in a collection of objects or in a DataSet object. The lesson introduces the basic syntax of LINQ queries, and summarizes the new language features in Microsoft Visual Basic® development system and Microsoft Visual C#® development tool that can be used to support and simplify LINQ queries.

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Introduction to LINQ

Key Points LINQ enables you to access data consistently, regardless of the origins of the data. Instead of having to use specific and disparate programming models to access data from different data sources, you can define LINQ queries that treat the data consistently.

The .NET Framework enables you to define LINQ queries to access data in a collection of objects, a DataSet object, a Microsoft SQL Server® database, an entity in an Entity Data Model, or an XML document.

Additional Information: For more information about Entity Data Models, see Module 5, " Implementing an Entity Data Model by Using the ADO.NET Entity Framework," of this course.

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Defining a LINQ Query

Key Points LINQ introduces a set of keywords in Visual Basic and Visual C# that enable you to define queries on an enumerable data collection, such as a collection of objects.

A LINQ query specifies the following information:

• The enumerable collection that you want to query.

• A filter expression that specifies the items that you are interested in.

• Conditions that specify whether the results should be ordered or grouped.

• The type of object that you want to obtain from the query.

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Executing a LINQ Query and Accessing the Result

Key Points You can use a For Each loop (Visual Basic) or a foreach loop (Visual C#) to iterate over the enumerable result set returned by a LINQ query.

LINQ uses a deferred execution model, so the execution of the LINQ query is deferred until the application iterates over the result set. This means that exceptions might occur during iteration, not in the query itself.

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Querying Data in a DataSet by Using LINQ

Key Points LINQ to DataSet enables you to execute LINQ queries against a DataTable in a DataSet object. You can obtain the results as a collection of DataRow objects, or as a collection of objects of an anonymous type.

Question: If you do not use LINQ, how do you access the data in a DataSet object?

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Demonstration: Defining and Executing LINQ Queries

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Lesson 2 Retrieving Data by Using LINQ to SQL

LINQ to SQL enables you to access and modify data in a SQL Server database by using LINQ queries. To use LINQ to SQL, you define entity classes that map to tables in the database. You can then perform data operations by using the entity classes and object-oriented programming techniques, instead of using ADO.NET data access classes such as SqlConnection, SqlCommand and SqlDataReader.

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Defining Entity Classes

Key Points You define an entity class by following these steps:

1. Define a class and map it to a database table by using the Table attribute.

2. Define properties and map them to database columns by using Column attributes.

The Table and Column attributes are defined in the System.Data.Linq.Mapping namespace, and are located in the System.Data.Linq assembly.

Question: Why might the name of the entity class and its properties differ from the name of the database table and its columns?

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Retrieving Data by Using an Entity Class

Key Points To retrieve data by using an entity class, you create a DataContext object and invoke the GetTable generic method. The GetTable method returns a generic Table object containing entity objects from the database.

The DataContext class and the Table generic class are defined in the System.Data.Linq namespace, and are located in the System.Data.Linq assembly.

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Joining Entity Classes by Defining Associations

Key Points LINQ to SQL enables you to define associations between entity classes, to represent the relationships between tables in the database. You can then define LINQ queries that perform joins between associated entity classes.

Question: What many-to-one relationships might you want to model as entity class associations in your own applications?

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Navigating Associations

Key Points When you define associations between entity classes, you can define and execute LINQ to SQL queries to navigate the association in either direction, as follows:

• From a parent entity to its collection of child entities.

• From a child entity to its parent entity.

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Demonstration: Defining Entity Classes Programmatically

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Demonstration: Defining Entity Classes by Using the Object Relational Designer

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Lesson 3 Modifying Data by Using LINQ to SQL

LINQ to SQL enables you to insert, update, and delete objects in a table in a DataContext object. The changes are held in memory until you invoke the SubmitChanges method on the DataContext object, to submit the changes to the database.

When you save changes to the database, optimistic concurrency errors can occur if other users have made conflicting changes to the data in the database. The LINQ to SQL API enables you to catch these errors and either reject the changes or force them through to the database.

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Inserting, Updating, and Deleting Entity Objects

Key Points LINQ to SQL enables you to insert, update, and delete entity objects in a DataContext table. The modifications are not saved to the database until you invoke the SubmitChanges method on the DataContext object, as described in the following topic.

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Submitting Changes to the Database

Key Points When you insert, update, or delete entities in a DataContext table object, the changes are made to the in-memory objects. To submit the changes to the database, you must invoke the SubmitChanges method on the DataContext object.

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Handling Optimistic Concurrency Conflicts

Key Points When you submit entity changes to the database, concurrency conflicts occur if other users have made conflicting changes to the data in the database. LINQ to SQL enables you to specify which entity columns to test for concurrency conflicts, whether to fail as soon as a concurrency conflict is detected or attempt to complete all updates, and how to resolve each conflict that is detected.

Questions: Why might you specify that an entity member should not be tested for optimistic concurrency conflicts?

Which strategy do you think you would use to resolve concurrency conflicts in your own applications?

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Lab: Querying and Maintaining Data by Using LINQ to SQL

Exercise 1: Defining Entity Classes

Scenario You are a developer for the Medical Clinic Management System for Contoso, Ltd. The Contoso Clinic Management System is a healthcare system for hospitals and clinics that run specialist practices. In this lab, you will add LINQ to SQL support to a Windows Forms application named PrescriptionManager, to enable the user to view and edit prescriptions for patients.

In this exercise, you will use the Object Relational Designer in Microsoft Visual Studio® 2008 to generate entity classes named Patient and Prescription, to represent the following tables in the Contoso Medical database:

Database Table Description

Patients Contains information about all the patients registered at the Contoso Medical Clinic.

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Database Table Description

Prescriptions Contains the following information about prescriptions:

• PrescriptionID. Primary key

• PatientID. Foreign key to a patient in the Patients table

• Description. Textual description of the prescription

• IssueDate. Date when the prescription was first issued

• RepeatCount. Number of times the prescription has been repeated.

You will define an association between the Patient and Prescription entity classes to represent the one-to-many relationship between patients and prescriptions.


1. Open the PrescriptionManager application.

2. Generate LINQ to SQL entity classes.

3. Define an association between entity classes.

4. View the generated classes.

Task 1: Open the PrescriptionManager application 1. Open Visual Studio 2008.

2. If you are using Visual Basic, open the solution E:\Labfiles\Starter\VB\PrescriptionManager\ PrescriptionManager.sln. If you are using Visual C#, open the solution E:\Labfiles\Starter\CS\PrescriptionManager \PrescriptionManager.sln.

Task 2: Generate LINQ to SQL entity classes 1. In the PrescriptionManager project, add a new LINQ to SQL project item

named ContosoMedicalDataClasses.dbml.

Verify that Visual Studio displays ContosoMedicalDataClasses.dbml in the Object Relational Designer window.

2. In Server Explorer, open a connection to the ContosoMedicalDB database on the local instance of Microsoft SQL Server® 2005 Express Edition.

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3. Generate an entity class to represent the Patients database table, by dragging the Patients table from Server Explorer to the Object Relational Designer surface.

Verify that the Object Relational Designer displays a box named Patient. This is the entity class that corresponds to the Patients database table.

4. Delete the Photo property in the Patient entity class, because the application does not need to access or view this information.

5. Generate an entity class to represent the Prescriptions database table, by dragging the Prescriptions table from Server Explorer to the Object Relational Designer surface.

Verify that the Object Relational Designer displays a box named Prescription. This is the entity class that corresponds to the Prescriptions database table.

Task 3: Define an association between entity classes 1. In the Object Relational Designer, define a one-to-many association between

the Patient entity class and the Prescription entity class. The association must link the PatientID primary key in the Patient entity class to the PatientID foreign key in the Prescription entity class.

2. Verify that the Object Relational Designer displays a one-to-many association between the Patient and Prescription entity classes. The association appears as an arrow from the Patient box to the Prescription box.

Task 4: View the generated classes 1. In Solution Explorer, open ContosoMedicalDataClasses.designer.vb (Visual

Basic) or ContosoMedicalDataClasses.designer.cs (Visual C#).

2. Locate the ContosoMedicalDataClassesDataContext class. This is a typed DataContext class that provides type-safe access to tables of Patient and Prescription entity objects. The following table describes some of the members in the ContosoMedicalDataClassesDataContext class.

Member Description

Patients Gets a table of Patient entity objects

Prescriptions Gets a table of Prescription entity objects

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3. Locate the Patient class. This is an entity class that maps to the Patients table in the ContosoMedicalDB database. The following table describes some of the members in the Patient class.

Member Description

_Prescriptions Instance variable that contains an EntitySet of Prescription entities for a patient

PatientID Property mapped to the PatientID column

FirstName Property mapped to the FirstName column

LastName Property mapped to the LastName column

Gender Property mapped to the Gender column

DateOfBirth Property mapped to the DateOfBirth column

Prescriptions Property that gets or sets the prescriptions for the patient. This property is annotated with an Association attribute that describes the one-to-many association between the Patient and Prescription entity classes.

4. Locate the Prescription class. This is an entity class that maps to the

Prescriptions table in the ContosoMedicalDB database. The following table describes some of the members in the Prescription class.

Member Description

_Patient Instance variable that contains an EntityRef that refers to the Patient entity for a prescription

PrescriptionID Property mapped to the PrescriptionID column

PatientID Property mapped to the PatientID column

Description Property mapped to the Description column

IssueDate Property mapped to the IssueDate column

RepeatCount Property mapped to the RepeatCount column

Patient Property that gets or sets the patient for the prescription. This property is annotated with an Association attribute that describes the one-to-many association between the

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Member Description

Patient and Prescription entity classes.

Results: After this exercise, you should have generated entity classes for the Patients and Prescriptions tables in the ContosoMedicalDB database, and defined a one-to-many association between the entity classes.

Exercise 2: Retrieving Data by Using LINQ to SQL In this exercise, you will use the Patient and Prescription entity classes to retrieve and display data from the database. You will enable the user to view prescriptions for a particular patient or for a particular period, as follows:

• When the PrescriptionManager application starts, you will use LINQ to SQL to get all of the patients from the database and display them in a DataGridView control.

• When the user clicks a patient record in the DataGridView control, you will execute a LINQ to SQL query to get the prescriptions for that patient. You will display the prescriptions in another DataGridView control.

• When the user requests prescriptions for a particular period, you will execute a LINQ to SQL query to get all of the prescriptions that were issued in that period. You will also use the association between the Prescription and Patient entity classes to retrieve the name of the patient associated with each prescription.


1. Review the user interface in the application.

2. Retrieve all of the patient records.

3. Retrieve prescriptions for a particular patient.

4. Retrieve prescriptions for a particular period.

Task 1: Review the user interface in the application 1. In Solution Explorer, in the PrescriptionManager project, open MainForm.vb

(Visual Basic) or Mainform.cs (Visual C#) in the form designer.

2. Review the following features in the View by Patient tab in the form:

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• The upper DataGridView control, patientsGridView, displays all of the patient records when the application starts.

• The lower DataGridView control, prescriptionsGridView, displays the prescriptions for a particular patient.

• The Repeat Prescriptions, Delete Prescriptions, and New Prescription buttons enable the user to modify prescription data. You will implement these features in the next exercise.

3. Click the View by Date tab in the form, and review the following features:

• The date picker controls, fromDatePicker and toDatePicker, enable the user to specify a date range.

• When the user clicks Go, the application retrieves the prescriptions in the specified date range and displays them in the prescriptionsInPeriodGridView control.

Task 2: Retrieve all of the patient records 1. In Solution Explorer, view the code for the MainForm form.

2. In the Variables, initialization, and selection events code region, locate the TODO: Create typed DataContext object. Add code to create a new ContosoMedicalDataClassesDataContext object, and assign the new object to an instance variable named _db.

3. In the View by Patient tab - display data code region, locate the DisplayPatients method. Where indicated by the TODO comment, add code to get and display all of the patient records from the database, as follows:

a. Define a For Each loop (Visual Basic) or a foreach loop (Visual C#) to iterate over the entities in the _db.Patients table.

b. On each iteration, create a string that contains the full name of the patient by concatenating the FirstName and LastName properties on the entity. Then add a row to the patientsGridView control, which contains the PatientID and full name of the patient.

Note: To add a row to the patientsGridView control, invoke the patientsGridView.Rows.Add method.


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5. Verify that the Prescription Manager window appears, and that the upper DataGridView control displays 18 patients.

6. Close the Prescription Manager window.

Task 3: Retrieve prescriptions for a particular patient 1. In the MainForm source file, locate the DisplayPrescriptions method.

The application invokes this method when the user highlights a patient on the form. The purpose of the method is to get all of the prescriptions for the highlighted patient, and display them in the prescriptionsGridView control on the form.

2. Where indicated by the first TODO comment, add code to define a LINQ query to get the prescriptions for the highlighted patient. Use the following information to help you to define the LINQ query:

• Specify _db.Prescripitons as the data source for the query.

• Define a Where clause (Visual Basic) or a where clause (Visual C#) that compares the PatientID for prescriptions with the patientID local variable, so that the query only returns prescriptions for that patient.

3. Where indicated by the second TODO comment, add code to display the prescriptions returned by the LINQ query, as follows:

a. Define a For Each loop (Visual Basic) or a foreach loop (Visual C#) to iterate over the LINQ query that you defined in the previous step.

b. On each iteration, add a row to the prescriptionsGridView control, which contains the PrescriptionID, Description, IssueDate, and RepeatCount properties for the prescription.


5. Verify that the Prescription Manager window appears, and that the upper DataGridView control displays 18 patient records. Also verify that the lower DataGridView control displays the prescriptions for the first patient.

6. In the upper DataGridView control, highlight the second patient. Verify that the lower DataGridView control now displays the prescriptions for the second patient.


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Task 4: Retrieve prescriptions for a particular period 1. In the MainForm source file, in the View by Date tab - display data code

region, locate the go_Click method.

The application invokes this method when the user clicks the Go button on the View by Date tab in the form, to get and display prescriptions in a particular period. Review the code that is already provided in the method.

2. Where indicated by the TODO comment, add the code provided in the Ex2_Task4.txt file that is located in the following folder:

• E:\Labfiles\Starter\VB (Visual Basic)

• E:\Labfiles\Starter\CS (Visual C#)

The code performs the following tasks:

a. Defines a LINQ query that gets the prescriptions in the specified date range, ordered by issue date.

b. Iterates over the query results, and displays each prescription in the prescriptionsInPeriodGridView control. The code gets the name of the patient for each prescription by using the Patient.FirstName and Patient.LastName properties on the prescription entity.


4. In the Prescription Manager window, click the View by Date tab.

5. View the prescriptions between January 1, 2008 and March 31, 2008. Verify that the application displays the prescriptions in the specified date range.

6. View the prescriptions between April 1, 2008 and June 30, 2008. Verify that the application displays the prescriptions in the specified date range.


Results: After this exercise, you should have defined and executed LINQ to SQL queries to get information about patients and prescriptions from the ContosoMedicalDB database.

Exercise 3: Modifying Data by Using LINQ to SQL In this exercise, you will enhance the PrescriptionManager application so that it enables the user to add, modify, and delete prescriptions. When the application submits the changes to the database, the application will check for optimistic concurrency conflicts. If such conflicts arise, the application will inform the user of

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the conflict, and will continue trying to submit the remaining changes to the database.


1. Get a specific Prescription entity.

2. Update a Prescription entity.

3. Delete a Prescription entity.

4. Insert a Prescription entity.

5. Save changes to the database.

6. Test the application.

Task 1: Get a specific Prescription entity 1. In the MainForm source file, in the View by Patient tab - modify data code

region, locate the TODO: Define a GetPrescriptionEntity method comment.

2. Add the code provided in the Ex3_Task1.txt file that is located in the following folder:



The code defines the GetPrescriptionEntity method, which performs the following tasks:

a. Defines a LINQ query that gets the prescription that matches the specified prescription ID.

b. Invokes the First method on the LINQ query to retrieve the first, and only, entity in the query result set.

You will use the GetPrescriptionEntity method in the following tasks, to locate a Prescription entity that is to be updated or deleted.

Task 2: Update a Prescription entity 1. In the MainForm source file, locate the repeatPrescriptions_Click method.

The application invokes this method when the user clicks Repeat Prescriptions on the form. The purpose of the method is to increment the

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RepeatCount property for Prescription entities that are highlighted by the user. Review the code that has already been provided in the method.

2. Where indicated by the first TODO comment, add code to invoke the GetPrescriptionEntity method to get the Prescription entity for the prescriptionID.

3. Where indicated by the second TODO comment, add code to increment the RepeatCount property on the Prescription entity.

Note: At the end of the repeatPrescriptions_Click method, the application invokes the DoSave method. You will implement this method later in this exercise, to submit the changes to the database.

4. Build the application and verify that no errors or warnings occur.

Task 3: Delete a Prescription entity 1. In the MainForm source file, locate the deletePrescriptions_Click method.

The application invokes this method when the user clicks Delete Prescriptions on the form. The purpose of the method is to mark a Prescription entity for deletion. Review the code that has already been provided in the method.

2. Where indicated by the first TODO comment, add code to invoke the GetPrescriptionEntity method to get the Prescription entity for the prescriptionID.

3. Where indicated by the second TODO comment, add code to mark the Prescription entity for deletion from the _db.Prescriptions table.

Task 4: Insert a Prescription entity 1. In the MainForm source file, locate the newPrescriptions_Click method.

The application invokes this method when the user clicks New Prescriptions on the form. The purpose of the method is to enable the user to create new prescriptions for a patient.

2. Where indicated by the TODO comment, uncomment the code that creates and displays a NewPrescriptionsForm form.

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3. In Solution Explorer, open NewPrescriptionForm.vb (Visual Basic) or NewPrescriptionForm.cs (Visual Basic) in the form designer.

The form enables the user to select a date, and to create a series of prescriptions issued on that date. Each time the user clicks Add, the form creates another Prescription entity and adds it to the DataContext. When the user clicks Done, the application returns to the main form.

4. View the code for the NewPrescriptionForm form.

5. In the NewPrescriptionForm source file, where indicated by the first TODO comment, add code to declare a ContosoMedicalDataClassesDataContext instance variable named _db.

6. Where indicated by the second TODO comment, add the code provided in the Ex3_Task4_Constructor.txt file that is located in the following folder:



The code defines a constructor that initializes the _patientID and _db instance variables. The form needs this information so that it can locate a particular Patient entity and then add Prescription entities to the DataContext.

7. Locate the add_Click method. The application invokes this method when the user clicks Add. Where indicated by the TODO comment, add the code provided in the Ex3_Task4_CreatePrescription.txt file that is located in the following folder:



The code creates and initializes a Prescription entity, marks it for insertion into the DataContext, and then displays the prescription description on the form.

Task 5: Save changes to the database 1. Switch to the MainForm source file, and locate the Do Save method.

2. Where indicated by the TODO: Submit changes to the database comment, add code to invoke the SubmitChanges method on the _db object. Pass ConflictMode.ContinueOnConflict into the method, so that the DataContext object attempts to complete all of the updates even if concurrency conflicts occur.

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3. Where indicated by the TODO: Catch ChangeConflictException exceptions comment, add the code provided in the Ex3_Task5.txt file located in the following folder:




a. Catches ChangeConflictException exceptions, which indicate that a concurrency conflict has occurred.

b. Iterates over the collection of change conflicts, and displays information about the object that caused a concurrency conflict; the members in conflict; and the current, original, and database values of each such member.

c. Invokes the Resolve method to refresh the current values in memory with the latest values from the database.

Task 6: Test the application 1. Build the application. Verify that no errors or warnings occur.

2. Run the application.

3. Update several prescriptions for the first patient, as follows:

a. In the lower DataGridView control, highlight several prescriptions, and then click Repeat Prescriptions.

b. Verify that the application increases the RepeatCount for each highlighted prescription. Make a note of the prescriptions that you updated.

4. Delete several prescriptions for the first patient, as follows:

a. In the lower DataGridView control, highlight several prescriptions, and then click Delete Prescriptions.

b. Verify that the application deletes each of the prescriptions that you highlighted. Make a note of the prescriptions that you deleted.

5. Add several new prescriptions for the first patient, as follows:

a. Click New Prescriptions.

b. In the New Prescriptions for PatientID 1 dialog box, in the Issue date control, select the current date.

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c. In the Description box, type a description for a new prescription, and then click Add.

d. Verify that the Added box displays the description that you just typed. This verifies that the application has created a new prescription.

e. Repeat the previous two steps several times, to create several prescriptions.

f. Click Done to return to the main form.

g. Verify that the application displays the new prescriptions that you just added. Make a note of the new prescriptions.


7. In Visual Studio, on the Debug menu, click Start Without Debugging to start the application again.

8. In the upper DataGridView control, click the first patient record. Verify that the lower DataGridView control shows the correct set of prescriptions for the patient, taking into account the prescriptions that you updated, deleted, and added earlier in this task.

9. In the lower DataGridView control, highlight several prescriptions. Do not click any buttons to affect the prescriptions yet; you will do so later in this task.

10. Switch back to Visual Studio. On the Debug menu, click Start Without Debugging to start another instance of the application.

11. In the upper DataGridView control, click the first patient.

12. In the lower DataGridView control highlight a subset of the prescriptions that you highlighted in Step 9, and then click Repeat Prescriptions to update these prescriptions.

13. Repeat the previous step several times, to update the RepeatCount property several times.

14. Close the second instance of the application, and return to the first instance of the application.

15. Click Repeat Prescriptions to update the highlighted prescriptions. Verify that the application detects and resolves optimistic concurrency conflicts as follows:

• For the prescriptions that you modified in the other instance of the application, the current instance of the application should display a

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message box, which indicates that an optimistic concurrency conflict has occurred. The message box should indicate the current, original, and database values of the RepeatCount property, and then update the value in the application with the value from the database.

• For the prescriptions that you did not modify in the other instance of the application, the current instance of the application should update the prescriptions successfully.



Results: After this exercise, you should have implemented functionality to enable the user to insert, update, and delete entities by using LINQ to SQL, and to detect and resolve optimistic concurrency conflicts.

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Review Questions 1. What are the benefits of using LINQ to SQL rather than using ADO.NET

classes such as SqlConnection and SqlCommand?

Using LINQ to SQL can be more productive for developers than using ADO.NET classes. Developers can define simple queries and delegate the complexities of database interactions to the LINQ to SQL provider.

2. What attributes do you use to designate a class as an entity class, and to specify that a member maps to a database column?

To specify that a class is an entity class, annotate the class with the Table attribute. To specify that a member maps to a database column, annotate the member with the Column attribute?

3. How do you define an association between two entity classes?

In the parent class, define an EntitySet instance variable and a property to get and set it. In the child class, optionally define an EntityRef instance variable

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and a property to get and set it. Annotate the properties in the parent and child classes with an Association attribute.

4. How do you insert and delete entity objects into a DataContext? How do you submit the changes to the database?

To insert an entity object into a DataContext, create an entity object and pass it as a parameter to the InsertOnSubmit method on the DataContext object.

To delete an entity object from a DataContext, pass it as a parameter to the DeleteOnSubmit method on the DataContext object.

To submit the changes to the database, invoke the SubmitChanges method on the DataContext object.

Common Issues Related to Accessing Databases With ADO.NET The following table lists some of the common problems you may get when using LINQ to SQL.



When you invoke the SubmitChanges method on the DataContext object, catch ChangeConflictException exceptions. For each entity object that causes a concurrency conflict, invoke the resolve method to specify whether you want to force the current values through to the database, keep the current values in memory, or load the latest values from the database.

Automatic key generation If you add entity objects to a DataContext, any database-generated values are not be assigned until you save the entity to the database. Do not attempt to use these values in your application until you save the changes.

Cascaded deletes LINQ to SQL does not support cascaded delete operations. For example, if you delete a Patient entity, LINQ to SQL does not automatically delete all of the associated Patient entities. You must add code to perform the cascaded deletion manually.

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Best Practices for Using LINQ to SQL Supplement or modify the following best practices for your own work situations:

• Retain entity changes in memory for as short a time as possible. Submit the changes to the database as soon as possible, to minimize the risk of concurrence conflicts with other users.

• Enclose updates in a transaction if appropriate, for example, to ensure all data is updated or no data updates.

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ITED Implementing an Entity Data Model by Using the ADO.NET Entity Framework 5-1

Module 5 Implementing an Entity Data Model by Using the ADO.NET Entity Framework

Contents: Lesson 1: Creating an Entity Data Model by Using the ADO.NET Entity Framework 5-3

Lesson 2: Querying and Modifying Data by Using the ADO.NET Entity Framework 5-9

Lab: Implementing an Entity Data Model by Using the ADO.NET Entity Framework 5-17

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ITED5-2 Implementing an Entity Data Model by Using the ADO.NET Entity Framework

Module Overview

The ADO.NET Entity Framework enables you to create data access applications by programming against a conceptual application model instead of programming directly against a relational storage schema. The goal of the ADO.NET Entity Framework is to decrease the amount of code and maintenance that is required for data-oriented applications.

This module describes how to create an Entity Data Model by using the ADO.NET Entity Framework, and how to query and modify data by using the Entity Framework.

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Lesson 1 Creating an Entity Data Model by Using the ADO.NET Entity Framework

This lesson describes how to how to create an Entity Data Model (EDM) by using tools provided by the ADO.NET Entity Framework.

An EDM contains a conceptual model that defines entity types that you use in your application, and a storage model that describes how the data is stored in the database. The EDM also contains a mapping specification that connects the entity types in the conceptual model to the database metadata in the storage model.

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Overview of the ADO.NET Entity Framework

Key Points The ADO.NET Entity Framework is a set of technologies that supports development of data-oriented software applications. The Entity Framework enables developers to work with data in the form of domain-specific objects and properties, such as customers and customer addresses, without having to consider the underlying database tables and columns where this data is stored.

The ADO.NET Entity Framework reduces the amount of data access code in object-oriented data applications and services, and makes it faster to create object-oriented data applications and services from an existing database.

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Entity Data Models

Key Points An .edmx Entity Data Model file defines the following information:

• Conceptual model

• Storage model

• Mapping specification

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Defining an Entity Data Model

Key Points The Entity Framework provides the tools that enable you to create and modify an EDM. The EMD can be created for a console, a Windows application or an ASP.NET applications.

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Demonstration: Creating an Entity Data Model

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Demonstration: Modifying an Entity Data Model

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Lesson 2 Querying and Modifying Data by Using the ADO.NET Entity Framework

The ADO.NET Entity Framework includes a component named Object Services that enables you to query and modify data in an Entity Data Model. This lesson describes the features provided by Object Services, and introduces a number of techniques for using entities in your application.

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Overview of Object Services

Key Points Object Services is a component of the Entity Framework that enables you to query, insert, update, and delete data, expressed as strongly-typed objects that are instances of entity types. Object Services supports both Entity SQL and LINQ to Entities queries against types that are defined in an EDM.

Object Services represents data from the data store as objects, and propagates object changes back to the persisted data store. Object Services also provides facilities for tracking changes, binding objects to controls, and handling concurrency.

Object Services is implemented by classes in the System.Data.Objects and System.Data.Objects.DataClasses namespaces.

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Defining Object Queries

Key Points The Entity Framework provides a generic class named ObjectQuery that enables you to execute queries against an EDM and return data as objects.

The ObjectQuery class provides a set of query builder methods, such as Where and Include, that enable you to filter and shape the query results.

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Using LINQ to Entities in Object Queries

Key Points LINQ to Entities enables you to define LINQ queries on the entities that are returned by an object query. In a typical scenario, an application defines an object query to retrieve data from the persistent data store into a collection of entities in memory, and then uses LINQ to Entities to query the entities without requiring additional roundtrips to the database.

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Using Entity SQL in Object Queries

Key Points Entity SQL is an SQL-like language that is provided by the Entity Framework and enables you to query and manipulate rich graphs of objects that are based on the EDM.

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Modifying Entities

Key Points The ObjectContext class provides methods that enable you to insert and delete entities in the cache of entities held in memory by the object context object. You can also locate existing entities and modify their property values in memory.

To save entity changes to the persistent data store, you must invoke the SaveChanges method on the ObjectContext object and handle any concurrency errors that might occur.

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Demonstration: Querying and Modifying Entities

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Demonstration: Binding Entities to Controls

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Lab: Implementing an Entity Data Model by Using the ADO.NET Entity Framework

Exercise 1: Creating an Entity Data Model

Scenario You are a developer for the Medical Clinic Management System for Contoso, Ltd. The Contoso Clinic Management System is a healthcare system for hospitals and clinics that run specialist practices.

In this exercise, you will define an Entity Data Model (EDM) to represent the Patients and Prescriptions tables in the ContosoMedicalDB database. In the other exercises in this lab, you will add code to the application to query and modify entities, by using object queries and Entity SQL.


1. Open the PrescriptionManager application.

2. Generate an Entity Data Model.

3. Define an association between the entities.

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4. Map the association between entities.

Task 1: Open the PrescriptionManager application 1. Open Microsoft Visual Studio 2008.

2. If you are using Visual Basic, open the solution E:\Labfiles\Starter\VB\PrescriptionManager\ PrescriptionManager.sln. If you are using Visual C#, open the solution E:\Labfiles\Starter\CS\PrescriptionManager \PrescriptionManager.sln.

Task 2: Generate an Entity Data Model 1. In Solution Explorer, in the PrescriptionManager project, add a new

ADO.NET EDM named ContosoMedicalModel.edmx.

2. When the Entity Data Model Wizard dialog box appears, generate the EDM from the ContosoMedicalDB database on the local instance of SQL Server Express, and add the Patients and Prescriptions tables to the EDM.

Verify that Visual Studio displays the ContosoMedicalModel.edmx file in the EDM designer window, and that the EDM contains boxes named Patients and Prescriptions.

3. In the designer, in the Patients entity, delete the Photo scalar property. The application does not require the photograph of the patient.

4. In the Patients entity, set the Name and Entity Set Name properties to Patient, to indicate that the entity represents a single patient.

5. In the Prescriptions entity, set the Name and Entity Set Name properties to Prescription, to indicate that the entity represents a single prescription.

Task 3: Define an association between the entities 1. In the designer, right-click the upper section of the Patient box, point to Add,

and then click Association.

2. In the New Association dialog box, verify that the default options represent a one-to-many association between the Patient and Prescription entities, and then click OK.

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3. Verify that the designer displays a one-to-many association between the Patient and Prescription entities. The association appears as a line between the Patient and Prescription boxes.

Task 4: Map the association between entities 1. In the designer, right-click the PatientPrescription association, and then click

Show in Mapping Details.

2. In the Mapping Details - PatientPrescription window at the bottom of Visual Studio, expand the <Add a Table or View> list, and then click Prescriptions.

Note: When you map an association, you must select the table that contains the foreign keys for the association in the database. In this example, the Prescriptions database table contains foreign keys to the Patients database table, to identify the patient for each prescription.

3. Verify that the Mapping Details - PatientPrescription window defines the following mapping information:

• For the Patient entity, the PatientID (Int32) entity property is mapped to the PatientID (int) column in the database table.

• For the Prescription entity, the PrescriptionID (Int32) entity property is mapped to the PrescriptionID (int) column in the database table.

4. In the main designer window, in the Prescription entity box, delete the PatientID scalar property.

The Prescription entity does not need the PatientID scalar property any more, because the Patient navigation property now defines the navigability from a Prescription entity to its associated Patient entity in memory.

5. Build the solution, and verify that there are no compiler errors or warnings.

Results: After this exercise, you should have generated an EDM that represents the Patients and Prescriptions tables in the ContosoMedicalDB database, and defined a one-to-many association between the entities in the EDM.

Exercise 2: Querying Entities in an Entity Data Model In this exercise, you will add code to the application to query entities in the EDM, as follows:

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• When the PrescriptionManager application starts, you will define an object query to get Patient entities for all of the patients in the database, and then bind the entities to a DataGridView control.

• When the user clicks a patient in the DataGridView control, you will define an object query to get the prescriptions for that patient. You will display the prescriptions in another DataGridView control.


1. Review the user interface in the application.

2. Retrieve patients.

3. Retrieve prescriptions.

Task 1: Review the user interface in the application 1. In Solution Explorer, in the PrescriptionManager project, open MainForm.vb

(Visual Basic) or Mainform.cs (Visual C#) in the form designer.

2. Review the following features in the form:

• The upper DataGridView control, patientsGridView, displays all of the patients when the application starts.

• The lower DataGridView control, prescriptionsGridView, displays the prescriptions for a particular patient.

• The Repeat Prescriptions button enables the user to modify selected prescriptions, by incrementing their RepeatCount property.

Note: For simplicity, the application does not enable the user to insert or delete prescriptions.

Task 2: Retrieve patients 1. Open the code file for the MainForm form.

2. At the top of the source file, where indicated by the first TODO comment, import the EDM namespace that you generated in the first exercise. The namespace to import is as follows:

• Visual Basic: PrescriptionManager.ContosoMedicalDBModel

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• Visual C#: ContosoMedicalDBModel

3. At the top of the source file, where indicated by the second TODO comment, import the System.Data.Objects namespace.

4. In the MainForm class, expand the Display data code region, and then locate the DisplayPatients method.

The application invokes this method during startup, to display the patients in the patientsGridView control.

5. Where indicated by the TODO comment, add the code provided in the Ex2_Task2.txt file located in the following folder:

• If you are using Visual Basic: E:\Labfiles\Starter\VB

• If you are using Visual C#: E:\Labfiles\Starter\CS

The code creates a ContosoMedicalDBEntities object, and contains TODO comments that you will implement in the following steps.

6. Where indicated by the TODO: Define an object query comment, define an ObjectQuery object to get all Patient entities from the database.

7. Where indicated by the TODO: Bind the retrieved entities comment, bind the entities that are returned by the query to the patientsGridView control.


9. Verify that the Prescription Manager window appears, and that the upper DataGridView control displays 18 patients.


Task 3: Retrieve prescriptions 1. In the MainForm source file, locate the DisplayPrescriptions method.

The application invokes this method when the user highlights a patient on the form. The purpose of the method is to get all of the prescriptions for the highlighted patient, and display them in the prescriptionsGridView control on the form.

2. Where indicated by the TODO comment, add the code that is provided in the Ex2_Task3.txt file, which is located in the following folder:



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The code is complete, and performs the following tasks:

a. Creates a ContosoMedicalDBEntities object.

b. Defines an object query to get Prescription entities for the highlighted patient. The Where method uses the syntax it.Patient.PatientID to get the Patient entity that is associated with the current prescription, and then gets the PatientID property on the Patient entity. The Where method uses the PatientID property to retrieve prescriptions for a particular patient.

c. Iterates over the Prescription entities that are returned by the object query, and displays the information in the prescriptionsGridView control.


4. Verify that the Prescription Manager window appears, and that the upper DataGridView control displays 18 patients. Verify that the lower DataGridView control displays the prescriptions for the first patient.

5. In the upper DataGridView, click the second patient. Verify that the lower DataGridView control displays the prescriptions for the second patient.


Results: After this exercise, you should have defined and executed object queries to get information about patients and prescriptions from the ContosoMedicalDB database.

Exercise 3: Modifying Entities in an Entity Data Model In this exercise, you will enhance the PrescriptionManager application so that it enables the user to modify prescriptions. You will enable the user to select prescriptions for a patient, and then increment the RepeatCount property on the prescriptions.


1. Modify entities.

2. Test the application.

Task 1: Modify entities 1. In the MainForm source file, locate the repeatPrescriptions_Click method.

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The application invokes this method when the user clicks the Repeat Prescriptions button, to repeat selected prescriptions.

2. Review the code that is already provided in the method. The code creates a string variable named prescriptionIDs that contains a list of all of the prescription IDs that the user highlighted. You will use this list of prescription IDs in an Entity SQL query later in this task.

3. Where indicated by the TODO comment, add the code that is provided in the Ex3_Task1.txt file, which is located in the following folder:




a. Creates a ContosoMedicalDBEntities object.

b. Defines an Entity SQL string to get the highlighted Prescription entities. The WHERE and IN operators ensure that the query only retrieves the set of Prescription entities whose PrescriptionID is in the prescriptionIDs list.

4. Where indicated by the TODO: Create an object query to get the requested prescriptions comment, define an ObjectQuery object to retrieve Prescription entities by using the Entity SQL string. Ensure that the query overwrites any local entity values with the latest values from the database.

5. Where indicated by the TODO: For each Prescription entity, increase the RepeatCount comment, iterate over the Prescription entities that are returned by the object query. For each Prescription entity, increment the RepeatCount property.

6. Where indicated by the TODO: Save the changes to the database comment, add code to save the object context changes to the database.

Task 2: Test the application 1. On the Build menu, click Build Solution. Verify that no errors or warnings

occur.

2. On the Debug menu, click Run Without Debugging.

3. In the Prescription Manager window, verify that the upper DataGridView control displays 18 patients. Verify that the lower DataGridView control displays the prescriptions for the first patient.

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4. Click some of the rows in the lower DataGridView control, and then click Repeat Prescriptions. Verify that the application shows the incremented repeat count for the prescriptions.


6. In Visual Studio, on the Debug menu, click Run Without Debugging.

7. In the Prescription Manager window, verify that the upper DataGridView control displays 18 patients. Verify that the lower DataGridView control displays the prescriptions for the first patient, and that the repeat counts are the incremented values.



Results: After this exercise, you should have modified entities and saved the changes back to the database.

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Review Questions 1. What information does an .edmx Entity Data Model file contain?

The .edmx file defines the conceptual model, the logical model, and the mapping specification for the EDM.

2. How do you define an association between entities, and what information does the code generator add to the entity classes?

In the EDM designer window, you right-click an entity, point to Add, and then click Association. You must verify the multiplicity at both ends of the association. When you define an association, the code generator adds a navigation property to each entity, to enable you to navigate the association programmatically.

3. What is an object context?

An object context encapsulates the underlying connection to the database, so that you can execute object queries.

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4. When might you decide to use LINQ to Entities rather than executing a new object query?

LINQ to Entities is useful when you have already executed an object query to retrieve a collection of entities, and you want to obtain selective entities or properties from the result set in memory without performing another database roundtrip.

Common Issues related to the ADO.NET Entity Framework The following table lists some of the common issues that may arise when you use the ADO.NET Entity Framework.



When you invoke the SaveChanges method on the ObjectContext object, catch OptimisticConcurrencyException exceptions. Invoke the Refresh method on the the ObjectContext object, to specify how you want to handle the conflict.

Mapping associations When you map an association between two entities, you must delete the original scalar property that represented the foreign key. In its place, the code generator creates a navigation property that you can use to locate the associated entity.

Best Practices for the ADO.NET Entity Framework Supplement or modify the following best practices for your own work situations:

• Retain entity changes in memory for as short a time as possible. Submit the changes to the database as soon as possible, to minimize the risk of concurrent conflicts with other users.

• Make use of the advanced capabilities that are available in EDMs to abstract your code from the underlying database schema.

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ITED Building Occasionally Connected Solutions by Using Synchronization Services 6-1

Module 6 Building Occasionally Connected Solutions by Using Synchronization Services

Contents: Lesson 1: Understanding Microsoft Synchronization Services 6-3

Lesson 2: Downloading Data by Using Synchronization Services 6-7

Lesson 3: Uploading Data by Using Synchronization Services 6-12

Lab: Building Occasionally Connected Solutions by Using Synchronization Services 6-17

Course Evaluation 6-33

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Module Overview

Microsoft® Synchronization Services is a separate library, in addition to the Microsoft .NET Framework, that enables you to write code for applications that have one or more clients that connect occasionally. For example, you would use this library when you develop an application to run on a laptop that is usually not connected to the network.

In this module you will learn about the architecture and the Applications Programming Interface (API) of Synchronization Services and how to use the services to perform synchronization.

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Lesson 1 Understanding Microsoft Synchronization Services

This lesson describes the architecture of Synchronization Services, the types of changes that can be tracked, and the architecture of the code that is used to provide occasionally connected applications.

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Overview of Synchronization Services

Key Points Synchronization is the process where the data in one data source is used to update the data in another data source. Microsoft Synchronization Services provides ADO.NET classes to enable you to synchronize between data sources. The server side can be a data source for which there is an ADO.NET 2.0 data provider and the client side can be Microsoft SQL Server® or Microsoft SQL Server® Compact Edition 3.5 and later. Synchronization Services can handle multiple clients uploading and downloading data from a server simultaneously. The services ensure that only data that has changed since the last synchronization is exchanged, and indicates conflicts.

Question: How does the client find out that there have been changes in the server?

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Synchronization Models Supported by Synchronization Services

Key Points Synchronization Services supports four synchronization modes. You chose the mode that best suits your application.

Question: What are the principal differences between snapshot and download-only?

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Common Application Architectures that Use Synchronization Services

Key Points Synchronization Services supports two tier, n-tier, and service-based architecture.

Question: When could these models be applied to your own applications?

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Lesson 2 Downloading Data by Using Synchronization Services

This lesson explains how to change the server database to support Synchronization Services and how a client application can retrieve data by using Synchronization Services.

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Configuring a Server Database to Support Synchronization

Key Points You must alter the server database so that Synchronization Services can track changes. You do not make any changes to the client database.

Question: Why would you track user id?

Question: What changes must be made on the database to support tracking deleting rows?

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Overview of the Synchronization Services API

Key Points Synchronization Services provides classes to co-ordinate synchronization and to access data sources on the client and on the server.

Question: Which of these objects do you call on a server in an n-tier application?

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Downloading and Caching Data in a Client Database

Key Points Synchronization applies the changes made on one database over a period of time to another database. At synchronization time, Synchronization Services generates anchor values and uses these values to determine which rows have changed.

Question: Where do the values for anchor session variables come from?

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Demonstration: Downloading and Caching Data by Using Synchronization Services

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Lesson 3 Uploading Data by Using Synchronization Services

This lesson describes how your applications can upload data to the server. This lesson also explains how your applications are informed about synchronization conflicts and how you can handle these conflicts.

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Uploading Modified Data from a Client Database

Key Points When you use upload-only or bidirectional synchronization there is a possibility that more than one client could attempt to change the same row.

Question: Why can you not use transactions to solve the type of concurrency issue that occurs with synchronization?

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Detecting and Resolving Conflicts

Key Points The synchronization provider indicates conflicts by raising the ApplyChangeFailed event. You can resolve conflicts by changing the properties of the event argument.

Question: How can you reduce the possibility of conflicts during synchronization?

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Handling Synchronization Events

Key Points You can monitor the progress of the synchronization through events that are raised on the synchronization providers and the synchronization agent.

Question: What is the significance of the fact that the events that are used to monitor progress are raised on the thread that called Synchronize?

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Demonstration: Uploading Data by Using Synchronization Services

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Lab: Building Occasionally Connected Solutions by Using Synchronization Services

Exercise 1: Modifying a Database Schema to Support Synchronization

Scenario You are a developer for the Medical Clinic Management System for Contoso, Ltd. The Contoso Clinic Management System is a healthcare system for hospitals and clinics that run specialist practices.

In this lab you will write an application that enables doctors to view and edit their appointments. This application runs on the doctors' computers that are only occasionally connected to the database. A doctor can change some items, like the notes for each appointment, and cache these changes locally. When the doctor is connected to the database he can download new appointments and upload changes he has made to the appointments on his computer.

In this exercise you will alter the database to enable Synchronization Services to synchronize the database with locally cached tables on a doctor's computer.

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2. Add a Local Database Cache.

3. Examine the generated code.

4. Examine the database.


DEV-06.


Task 2: Add a Local Database Cache 1. Open Microsoft Visual Studio 2008.

2. If you are using Microsoft Visual Basic® development system, open the solution E:\Labfiles\Starter\VB\Appointments\Appointments.sln. If you are using Microsoft Visual C#® develpoment tool open the solution E:\Labfiles\Starter\CS\Appointments\Appointments.sln.

3. In the MobileAppointments project, add a new Local Database Cache item called client.sync

When you add this item the Configure Data Synchronization wizard will run.

4. In the Configure Data Synchronization wizard, perform these steps:

a. Add a new connection to ContosoMedicalDB on .\SQLEXPRESS

b. To the Cached tables control, add the Appointments table.

5. When the Configure Data Synchronization wizard completes, the Data Source Configuration Wizard allows you to add a dataset.

a. Add the Appointments table with the following columns:

• AppointmentID

• PatientID

• AppointmentDateTime

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• Notes

b. Change the DataSet name to clientDataSet.

6. Confirm that the wizard performs these steps:

a. Creates the SQL Server CE 3.5 database file, as the local cache, and adds it to the project.

b. Adds a dataset that you can use to connect to the local cache.

Task 3: Examine the generated code 1. View the code generated by the wizard for Synchronization Services. The

easiest way to do this is to use Class View to load the code for the clientClientSyncProvider class.

2. The Local Database Cache wizard has generated the following classes.

Class Description

clientClientSyncProvider This is the local synchronization provider and holds the code to connect to the local cache.

clientSyncAgent This is the synchronization agent that encapsulates the code to create the synchronization providers and to indicate which tables to synchronize.

clientSyncAgent .AppointmentsSyncTable

This class indicates the table that will be synchronized and the direction of the synchronization.

AppointmentsSyncAdapter This is the server synchronization adapter that indicates information about how to access the server database.

clientServerSyncProvider This is the server synchronization provider.

3. Scroll to the nested class clientSyncAgent.AppointmentsSyncTable. The

wizard only generates code to perform download-only synchronization. Notice the following:

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• The class does not explicitly declare the value for the SyncTable.SyncDirection property, so it uses the default which is DownloadOnly.

• The class calls the partial method OnInitialized in the constructor.

4. Add an implementation for the OnInitialized method of the clientSyncAgent.AppointmentsSyncTable. The code for this method is supplied in the Ex1_Task3_OnInitialized.txt file.



5. Add a line to enable you to use members from the Microsoft.Synchronization.Data namespace.

6. Save your code.

Task 4: Examine the database 1. In Solution Explorer, expand the ContosoNedicalDatabases project and

double-click lon-dev\SQLEXPRESS.ContosoMedicalDB.dbo.

2. In Server Explorer, expand lon-dev\SQLEXPRESS.ContosoMedicalDB.dbo and view the tables in the database. Notice that there is a new table called Appointments_Tombstone.

3. Examine the Appoinments table, note that there are two new columns, as described in the following table.

Item Description

LastEditDate A datetime column used to track when a row was last updated. This is a new column.

CreationDate A datetime column used to track when a row was inserted. This is a new column.

4. Examine the triggers created for the Appointments table.

Trigger Description

Appointments_DeletionTrigger Adds an entry in the tombstone table for the deleted row, together with the appointment identifier and the current time. If the row has

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Trigger Description

been deleted before then the tombstone entry is updated to show the current time.

Appointments_InsertTrigger Initializes the CreationDate column with the current time.

Appointments_UpdateTrigger Initializes the LastEditDate column with the current time.

5. Examine the Appointments_Tombstone table, summarized in the following

table.

Item Description

AppointmentID This is the primary key of the row that was deleted.

DeletionDate This is the time and date when the row was deleted.

Results: After this exercise, you should have altered the database to enable synchronization and generated supporting classes to initiate synchronization.

Exercise 2: Downloading Data to a Client Computer In this exercise you will add the code to synchronize the locally cached database with the server database. You will only support download-only synchronization.


1. Examine the user interface.

2. Alter the SyncAdapter class.

3. Add a new DataSet.

4. View the server test code.

5. Compile and test download-only synchronization.

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Task 1: Examine the user interface 1. Open MainForm.vb (Visual Basic) or MainForm.cs (Visual C#) in the forms

designer.

2. Examine the controls on this form as summaarized in the following table.

Control Description

doctorID Use this text box to provide the identifier for the doctor.

synchronize Click this button to synchronize between the server database and the local cache.

saveCache Click this button to save data in the grid to the local cache. (Will be used in a later exercise.)

appointmentsGrid View the data in the local cache.

Task 2: Alter the SyncAdapter class 1. Review the InitializeCommands on the AppointmentstSyncAdapter class

that was generated by the Configure Data Synchronization wizard. The commands defined in this method are summarized in the following table.

Command Description

InsertCommand This is called to insert a row in the server database. The command first sets the IDENTITY_INSERT T-SQL option so that a value can be provided for the identity row. The command then inserts a row into the table. All of the column values are provided through parameters. The command provides values for the date tracking columns, which is redundant because the insertion trigger will perform this action. Finally, the @sync_row_count session variable is initialized by the value of the number of rows inserted.

DeleteCommand The row that holds the specific AppointmentID value is deleted under one of two conditions: either this is a force write or the row was not edited since last synchronized. A force write means that the

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Command Description

client has indicated that the client changes must be made regardless of any conflicts with the server data. The AppointmentID value, which identifies the appointment row to be deleted, is provided through a parameter. The @sync_row_count session variable is initialized by the value of the number of rows inserted.

UpdateCommand The row with the specified AppointmentID is updated. All the other columns are provided through parameters, including the date tracking columns, which is redundant because the update trigger will perform this action. The update is performed under one of two conditions: either this is a force write or the row was not edited since last synchronized. The @sync_row_count session variable is initialized by the value of the number of rows inserted.

SelectConflictDeletedRowsCommand The query used to determine if there is a deletion conflict. This simply tests the tombstone table for a row with the specified AppointmentID value.

SelectConflictUpdatedRowsCommand The query used to identify updated rows that conflict with other changes.

SelectIncrementalInsertsCommand The query used to obtain the rows that were inserted since the last synchronization.

SelectIncrementalDeletesCommand The query used to obtain the rows that were deleted since the last synchronization.

SelectIncrementalUpdatesCommand The query used to obtain the rows that were updated since the last synchronization.

2. In Server Explorer, examine the uspGetAppointmentsForDoctor stored

procedure. This procedure is used to get all of the appointments for a specific doctor.

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3. To enable you to use the results from the stored procedure you will remove the local cache and the dataset that was generated for you.

a. Remove the ContosoMedicalDB.sdf file from the project.

b. Remove the ContosoMedicalDB.sdf file from the output build folder.

c. Remove the clientDataSet.xsd file from the project.

In the following steps you will generate new versions of these files.

4. Provide an implementation of OnInitialized in the AppointmentsSyncAdapter class to provide the commands to invoke the uspGetAppointmentsForDoctor stored procedure. The code for this method is in the Ex2_Task2_OnInitialized.txt file.

Task 3: Add a new DataSet 1. Recreate the cached database. Add an implementation for the Click handler of

the Synchronize button to create an empty Sql Server CE 3.5 database and use Synchronization Services to fill this database. The implementation of this method can be found in the Ex2_Task3_synchronize_Click.txt file.

2. Compile and run the application. Click Synchronize, to generate the new database file. Close the application.

3. Copy the generated file, ContosoMedicalDB.sdf, to the project folder and add it to the project. The Data Source Configuration Wizard starts to create a new dataset in the project. Add the dataset for Appointments table and call this dataset clientDataSet. Indicate that the dataset will use the following columns.

• AppointmentID

• AppointmentDateTime

• FullName

• Gender

• DateOfBirth

• Notes

4. Use the Appointments table on the clientDataSet dataset as the DataSource

value of the appointmentsGrid control on the MainForm form.

A table adapter and a binding source are generated.

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5. In the synchronize_Click method, update the data grid view by using the table adapter. Add the following line of code after the call to agent.Synchronize.

[Visual Basic] Me.appointmentsTableAdapter.Fill(Me.clientDataSet.Appointments)

[Visual C#] this.appointmentsTableAdapter.Fill(this.clientDataSet.Appointments);

Task 4: View the server test code 1. In Solution Explorer, open the DesktopAppointments project, and then open

the MainForm form in the forms designer.

2. Familiarize yourself with the controls on this form as summarized in the following table.

Control Description

navigator This navigation control enables you to navigate through the Appointments table on the server. In particular notice the following buttons:

• The Delete button deletes the selected row in the dataset.

• The Save button saves all of the changes in the dataset to the server database.

• The Refresh button reads the dataset from the database. If you have already made changes to the dataset they are discarded.

appointmentsGrid This data grid shows values from the Appointments table. If you add a new row, you must provide values for DoctorID, PatientID and AppointmentDateTime.

Task 5: Compile and test download-only synchronization 1. Compile and run the client application.

2. Start the server application.

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Note: Visual Studio only starts the process for the project that is marked as the startup project. To start processes created by other projects, you must start the process directly from the build output folder.

3. Position the applications side by side and compare the contents.

Verify that they are synchronized.

4. In the Desktop Calendar add the following rows. On the navigator, click the Add New button, and then fill all of the cells except for the AppointmentID cell. When you have entered the values for all of the new rows, click the Save button on the navigator.

a. Add the first new appointment.

Column Value

DoctorID 1

PatientID 5

AppointmentDateTime 06/03/2008 9:00

Notes First new appointment

b. Add the second new appointment.

Column Value

DoctorID 2

PatientID 10

AppointmentDateTime 06/03/2008 10:00

Notes Second new appointment

5. Verify that the Mobile Calendar application reads its data from the local cache

rather than the server database. Close the application, then restart and verify that there are no new rows.

6. On the Mobile Calendar form click Synchronize. Verify that the Mobile Calendar now has the row you entered on Desktop Calendar.

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7. In the Desktop Calendar, make a change to the Notes field for the row that you just inserted for doctor 1. Click the Save button. In the Mobile Calendar click Synchronize, and confirm that the change has been copied to the cached database.

8. In the Desktop Calendar, delete the new row. Click the Save button to save the results to the database. In the Mobile Calendar, click Synchronize, and confirm that the previous row has been deleted.

9. Close Mobile Calendar but keep Desktop Calendar running for the other exercises.

Results: After this exercise, you should have implemented an application that performs download-only synchronization with a SQL Server database. You should have shown that synchronization works for inserted, updated, and deleted rows.

Exercise 3: Uploading Data Changes to the Database In this exercise you will write the code to support bidirectional synchronization and to enable you to handle conflicts.


1. Change the MobileAppointments class to use bidirectional synchronization.

2. Add conflict handling.


Task 1: Change the MobileAppointments class to use bidirectional synchronization 1. In the code for the MainForm form, alter the OnInitialized method of the

nested class AppointmentsSyncTable so that the synchronization direction is bidirectional.

2. Provide a workaround for the InsertCommand method of the AppointmentsSyncAdapter class, which was generated by the wizard. The workaround code is in the Ex3_Task1_OnInitialized.txt file.

3. In the Forms Designer, double-click the Save Cache button on the MainForm form, and then add the following code to save the data in the data grid view control through the table adapter object.

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[Visual Basic] Me.Validate() Me.appointmentsBindingSource.EndEdit() Me.appointmentsTableAdapter.Update(Me.clientDataSet.Appointments)

[Visual C#] this.Validate(); this.appointmentsBindingSource.EndEdit(); this.appointmentsTableAdapter.Update(this.clientDataSet.Appointments);

4. Compile and run the application.

a. In Mobile Calendar change the Notes cell of one of the appointments.

b. Click Save to Cache to save the change to the local cache.

c. Click Synchronize to synchronize the changes to the server.

d. In Desktop Calendar, click Refresh and verify that the Notes column of the appointment that you changed has changed to the value you used.

e. Close the Mobile Calendar application.

Task 2: Add conflict handling 1. Open the Handle Conflict dialog in the forms designer and examine the

controls.

Control Description

The following conflict has occurred

This text box displays the conflict that has occurred. It gives the type of conflict and the conflicting client and server rows.

How do you want to handle this? This radio button group enbles you to determine if you will allow the default action to occur, or if you want to force another action.

2. View the code for this form. There are two properties:

a. The Action property returns an ApplyAction value based on the radio button selected.

b. The ConflictType property displays information about the conflict in the text box on the form.

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3. On the MainForm form, open the Click handler for the Synchronize button and, immediately before the call to agent.Synchronize(), add code to handle the ApplyChangeFailed event on the remote synchronization provider with a method called remore_ApplyChangeFailed.

The Ex3_Task2_ApplyChangeFailed.txt file has the implementation of remore_ApplyChangeFailed.

This code creates an instance of the Handle Conflict dialog and uses the results from this dialog to determine how the ApplyChangeFailed event is handled.

Task 3: Build and run the application 1. Click Build. Click Build Solution.

a. Add a new row to the server database by using Desktop Calendar.

b. On the navigator, click the Save button to save the data in the server database.

c. In Mobile Calendar synchronize the databases.

2. Generate a conflict as follows:

a. In Mobile Calendar, change the Notes cell for the new row, and then click Save to Cache to save this change in the cached database.

b. In Desktop Calendar, change the Notes cell for the same row, and then click Save to save the change in the server database.

c. In Mobile Calendar, click Synchronize.

The Handle Conflict dialog appears and shows the details of the conflict.

d. Select Continue with the current action, and then click OK to indicate that the server changes should be accepted.

Confirm that the client cache is updated with the results from the server.

3. Repeat the previous test but this time in the Handle Conflict dialog box, select Force this write.

This time the client change is accepted. To confirm this, in Desktop Calendar, click Refresh to refresh the grid with values from the server database.

4. Generate a conflict by deleting a row in the server and updating the same row in the cached database.

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a. In Desktop Calendar, select the new row, and then click Delete. Click Save.

b. In Mobile Calendar, change the Notes field for this row. Click Save to Cache.

c. Synchronize.

Confirm that a conflict is detected: Mobile Calendar updated a row that Desktop Calendar deleted.

d. In the Handle Conflict dialog box, select Force this write.

e. Confirm that the row remains in the local cache.

f. In Desktop Calendar, click Refresh, and confirm that the row has been re-inserted into the server database.

5. Close Desktop Calendar and close Mobile Calendar.

Results: After this exercise, you should have implemented the application so that it handles synchronization conflicts and you can specify whether changes in the client override changes in the server.

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Review Questions 1. Why is it important that values for time tracking anchor values are generated

by the server?

For synchronization to work, it is vital that the time source used by all of the code that can change data is the same. If different time sources are used, even a difference in a few milliseconds can prevent Synchronization Services from working. A single time source prevents this problem.

2. What role do transactions play in Synchronization Services?

Transactions can only be used within individual commands, for example to update the server. A transaction must not be used between the Synchronization Services commands.

3. What role does the tombstone table play?

The tombstone table has sufficient information about the rows that have been deleted for Synchronization Services to determine which rows have been deleted since the last synchronization. This table is not an archive of deleted

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data, all the tombstone table needs is to have the identity column of the table that it is associated with, tracking information (like the time the row was deleted), and the identifier of the user who deleted the row.

Real-World Issues and Scenarios The following real world scenarios benefit from a solution that uses Synchronization Services.

1. Courier services.

2. Utility meter readers.

3. Survey taking.

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