meljun cortes vb.net handout ado.net_vb.net_handout_part_i

Visual Basic .NET Programming

ADO.NET * Property of STI of 12

TOPIC TITLE: ADO.NET Specific Objectives: At the end of the topic session, the students are expected to: Cognitive:

1. Explain how ADO .NET comes about and identify its uses. 2. Explain the ADO .Net architecture. 3. Enumerate and identify the uses of the namespaces and

components involve in the .NET Data Providers. 4. Identify the use of the Connection object and cite the steps on

how to connect to a database. 5. Identify the use of the Command object and cite some ways on

how to execute commands and return data from a data source. 6. Identify the use of the DataReader object and explain the use of

Read and Get methods in retrieving data. 7. Identify the use of the DataAdapter object and cite the ways on

creating this object. Affective:

1. Listen to others with respect. 2. Participate in class discussions actively.

MATERIALS/EQUIPMENT:

o topic slides o OHP

TOPIC PREPARATION:

o Have the students research on the following: � ADO.Net � .NET Data Providers � Connection object � Command object � DataReader object � DataAdapter object

o It is imperative for the instructor to incorporate various kinds of teaching strategies while discussing the suggested topics. The instructor may use the suggested learning activities below to facilitate a thorough and creative discussion of the topic.

o Prepare the slides to be presented in the class.

TOPIC PRESENTATION: The topic will revolve around ActiveX Data Objects for the .Net Framework. This will be the suggested flow of discussion for the course topic:

1. Introduce to the students the topics to be covered in this session.

2. Ask the students to share their research about ADO .Net. 3. Explain what ADO.NET is. Also, present and explain the

ADO .Net Architecture. 4. Ask the students to tell something about .Net Data Providers. 5. Discuss the .NET Data Providers and give an overview of its

components.



6. Ask the students to identify the use of the Connection object. 7. Explain the Connection object as well as the steps to connect to

a database. Provide sample codes on how to connect to a SQL Server database and to an Access database.

8. Ask the students to identify the use of the Command object. 9. Explain the Command object and cite the methods on how to

create commands. Provide sample codes for each method 10. Enumerate and describe the methods used in executing

commands. Provide an example. 11. Ask the students to identify the use of the DataReader object. 12. Explain the DataReader object and discuss how to create a

read-only data stream. Provide sample codes using the Read and Get methods.

13. Ask the students to identify the use of the DataAdapter object. 14. Identify the use of the DataAdapter object and mention some

ways of creating this object. Provide sample codes for each. 15. Conduct Quiz #5.



What is ADO.NET? Page 1 of 19

ADO.NET


* Property of STIPage 1 of 19

What is What is What is What is ADO.NET?ADO.NET?ADO.NET?ADO.NET?

� ADO .Net

� group of libraries

� allow applications to read and update

information in databases and other sources

� includes two .NET data providers:

• SQL Server .NET Data provider

• OLE DB .NET Data Provider

Data Access Object

Remote Data Object

Active Data Object

ActiveX Data Object for .Net Framework

What is ADO.NET? The first data access model named DAO (Data Access Object) was created for local databases. This data access model had performance and functionality issues. Some of the issues in using DAO are speed, support limited number of users and since it is older technology as it runs best only in 16-bit environment. It has limited functionality as it does not have interface to e-mail, file systems and custom business objects. Then, RDO (Remote Data Object) and ADO (Active Data Object) came into the picture, which were designed for Client Server architectures. However, ADO was successful and took over RDO. With ADO, all the data is contained in a recordset object which had problems when implemented on the network and penetrating firewalls. ADO was a connected data access, which means that when a connection to the database is established the connection remains open until the application is closed. This raised concerns about database security and network traffic. Also, as databases are becoming increasingly important and as they are serving more people, a connected data access model makes us think about its productivity. For example, an application with connected data access may do well when connected to two clients, the same may do poorly when connected to 10 clients and might be unusable when connected to 100 clients or more. Also, open database connections use system resources to a maximum extent making the system performance less effective. To solve some of the problems mentioned above, ADO .NET came into existence. ADO .NET addresses the above mentioned problems by maintaining a disconnected database access model. ActiveX Data Objects for the .NET Framework (ADO.NET) is a set of classes or group of libraries that allow applications to read and update information in databases and other sources. It provides access to various data sources such as Microsoft SQL Server, OLE-DB compliant databases, MS Access, Oracle and XML. ADO.NET uses NET data providers to provide interface in the application to data sources. The Data Provider is responsible for providing and maintaining the connection to the database. It is a set of related components that work together to provide data in an efficient and performance-driven manner. It includes two .NET data providers namely SQL Server .NET Data provider and OLE DB .NET Data Provider. [What is ADO.NET, Page 1 of 19]



ADO.NET Architecture Page 2 of 19

ADO.NET



ADO.NET ADO.NET ADO.NET ADO.NET ArchitectureArchitectureArchitectureArchitecture

ADO.NET Architecture

The figure above shows the ADO.NET architecture which is divided into two logical entities namely command execution and caching. Command execution requires features like connectivity, execution, and reading of results. These features are enabled with .NET Data Providers. The DataSet handles caching of results. The .NET Data Provider enables connectivity and command execution to underlying data sources. Note that these data sources do not have to be relational databases. Once a command has been executed the results can be read using a DataReader. A DataReader provides efficient forward-only stream level access to the results. In addition, results can be used to render a DataSet a DataAdapter. The DataSet object represents a disconnected cache of data. The DataSet is a disconnected, in-memory representation of data. This cache is made up of DataTables and DataRelations that represent the results of the command. The DataSet tracks changes to the underlying data in the cache. Changes can be submitted back to the original data source by using the DataAdapter and applicable Insert, Update, or Delete commands. The DataSet also provides a direct XML view of the underlying data in the cache. [ADO.NET Architecture, Page 2 of 19]

.NET Data Providers Page 3 of 19

ADO.NET



.NET Data .NET Data .NET Data .NET Data ProvidersProvidersProvidersProviders

� System.Data.SQLClient namespace

� used for SQL Server 7.0 and later

databases

� System.Data.OleDb namespace

� used for all other databases

� Components:

� Connection object

� Command object

� DataReader object

� DataAdapter object

.NET Data Providers System.Data namespace consists mainly of classes that comprise the ADO.NET architecture. The System.Data.SQLClient namespace and the System.Data.OLEDB are the two namespaces that can be used to get access to different data sources. The first one is used to access SQL Server 7.0 and later databases and the latter is used to access any data sources that use the OLE DB. These providers contain four main objects that you can use to connect to a data source, read the data and manipulate the data. These four components are:

• Connection object – which provides a connection to the database

• Command object – which is used to execute a command

• DataReader object – which provides a forward-only, read only,



connected recordset

• DataAdapter object – which populates a disconnected DataSet with data and performs update

[.NET Data Providers, Page 3 of 19]

Connection Object Page 4 of 19

ADO.NET



Connection Connection Connection Connection ObjectObjectObjectObject

� creates the connection to the database

� connection classes:

� SqlConnection object

� OleDbConnection object

� Steps in connecting to a database:

� Set the connection type

� Specify the data source

� Connect to the data source

Connection Object The Connection object creates the connection to the database. Microsoft Visual Studio .NET provides two types of Connection classes namely the SqlConnection object, which is designed specifically to connect to Microsoft SQL Server 7.0 or later, and the OleDbConnection object, which can provide connections to a wide range of database types like Microsoft Access and Oracle. The Connection object contains all of the information required to open a connection to the database. There are three basic steps in connecting to a database. These are as follows:

1. Set the connection type. 2. Specify the data source. 3. Connect to the data source.

To achieve step 1, the Connection object is used to connect to a specific data source. Specifically, the SqlConnection and OleDbConnection objects are used for this purpose. After the connection type has been set, the ConnectionString property is used to specify the source database and other information used to establish the connection. Lastly, each Connection object supports an Open method that opens the connection after the connection properties have been set. It also has a Close method that is used to close the database connection. [Connection Object, 4 of 19]

SqlConnection Object Page 5 of 19

ADO.NET



SqlConnectionSqlConnectionSqlConnectionSqlConnectionObjectObjectObjectObject

� has a property that contains all the

information in establishing a connection

� ConnectionString property

� consists of name-value pairs

� Some common keywords used are:

� Connection Timeout / Connect Timeout

� Initial Catalog

� User ID

� Password / Pwd

� Data Source / Server/ Address / Addr /

Network Address

� Integrated Security / Trusted_Connection

SqlConnection Object

The SqlConnection object has a property that contains all the information in establishing a connection. This property is the

ConnectionString property that consists of name-value pairs providing the information required when connecting to a data source. The most commonly used name-value pairs in ConnectionString

property is shown below:

Name (Keyword) Default Value Description

Connection Timeout / Connect Timeout

15 seconds Delay for a connection to succeed before returning an error.

Initial Catalog None Name of the database

User ID None SQL server logon account

Password / Pwd None SQL server password

Data Source / Server/ Address / Addr / Network Address

None Name or address of SQL server

Integrated Security / Trusted_Connection

False Determines if the connection is a secure connection.



[SqlConnection Object, Page 5 of 19]

Example SQL Client .NET Data Provider Page 6 of 19

ADO.NET



Example:Example:Example:Example: SQL ClientSQL ClientSQL ClientSQL Client.NET Data Provider.NET Data Provider.NET Data Provider.NET Data Provider

Imports System

Imports System.Data.SqlClient

Module SQLClientDemo

Public Sub Main()

Dim strConnection As String =

“Integrated Security=True;Data

Source=Localhost;Initial

Catalog=Pubs;”

Dim conServer As SqlConnection =

New SqlConnection

conServer.ConnectionString =

strConnection

conserver.Open()

End Sub

End Module

Example: SQL Client .NET Data Provider Imports System



Public Sub Main()

Dim strConnection As String = “Integrated

Security=True;Data Source=Localhost;Initial

Catalog=Pubs;”

Dim conServer As SqlConnection = New SqlConnection

conServer.ConnectionString = strConnection

conserver.Open()

End Sub

End Module

The above example shows how to connect to a SQL Server database by using the SQL Client .NET Data Provider. To support a connection to a

database, the .NET Framework provides the SqlConnection class that

is defined in the System.Data.SqlClient namespace. The Imports

statements include this namespace in the file.

[Example SQL Client .NET Data Provider, Page 6 of 19]

OleDBConnection Page 7 of 19

ADO.NET



OleDbConnectionOleDbConnectionOleDbConnectionOleDbConnectionObjectObjectObjectObject

� uses a ConnectionString property similar

to SQLConnection but with some

additional keywords such as Provider,

URL, Remote Provider and Remote Server

Imports System

Imports System.Data.OleDb

Module OleDbDemo

Public Sub Main()


“Provider=Microsoft.Jet.OLEDB.4.

0;Data Source=C:\NWind.MDB”

Dim conServer As OleDbConnection

= New OleDbConnection


strConnection

conserver.Open()

End Sub

End Module

OleDbConnection The OleDbConnection object uses a ConnectionString property

similar to SQLConnection but with some additional keywords that is

now required. These keywords are Provider, URL, Remote

Provider and Remote Server. An example is shown below: Imports System

Imports System.Data.OleDb

Module OleDbDemo

Public Sub Main()


“Provider=Microsoft.Jet.OLEDB.4.0;Data

Source=C:\NWind.MDB”

Dim conServer As OleDbConnection = New

OleDbConnection


conserver.Open()

End Sub

End Module

The code above shows how to connect to an Access database by using the OLE DB .NET Data Provider. [OleDbConnection, Page 7 of 19]



Creating Commands Page 8 of 19

ADO.NET



Creating Creating Creating Creating CommandsCommandsCommandsCommands

� ADO.NET Command object is used to

execute commands

� SqlCommand

� used for SQL Server database

� OleDBCommand

� used for all other types of databases

� Ways to create a Command:

� use the Command constructor and pass the

Connection object as an argument

� use the CreateCommand method of the

Connection object

Creating Commands Page 9 of 19

ADO.NET



Creating Creating Creating Creating CommandsCommandsCommandsCommands

Imports System



Public Sub Main()




Catalog=Pubs;”

Dim conServer As SqlConnection = New

SqlConnection


strConnection

conserver.Open()

‘the code that will create a Command

Dim commSQL As SqlCommand = New

SqlCommand

commSql.Connection = conserver

commSql.Commandtext = “Select

count(*) from Employees”

End Sub

End Module

Creating Commands The ADO.NET Command object is used to execute commands. The

SqlCommand is used for SQL Server database and the OleDBCommand for all other types of databases. There are two ways to create a Command:

1. Using the Command constructor and pass the Connection

object as an argument.

2. Use the CreateCommand method of the Connection object

The Command object has a property named CommandText that can be used to set and retrieve SQL statement being executed. An example is shown below. The line of codes in italic represents the creation of the Command using the step 1 described above. Imports System



Public Sub Main()



Catalog=Pubs;”



conserver.Open()

‘the code that will create a Command

Dim commSQL As SqlCommand = New SqlCommand


commSql.Commandtext = “Select count(*) from

Employees”

End Sub

End Module

What follows are the lines of codes that represent the creation of the Command using the step 2 described above.

‘the code that will create a Command using

CreateCommand


commSql = conserver.CreateCommand


Employees

[Creating Commands, Pages 8-9 of 19]

Executing Commands There are four methods that can be used to execute a Command as follows:

1. ExecuteReader

2. ExecuteScalar

3. ExecuteNonQuery



Executing Commands Page 10 of 19

ADO.NET



Executing Executing Executing Executing CommandsCommandsCommandsCommands

� Methods used to execute a Command:

� ExecuteReader

• used when the query will return a stream of

data

� ExecuteScalar

• used when the query return a single value

� ExecuteNonQuery

• used when the query will not return a

result

� ExecuteXMLReader

• used when the query includes a valid FOR

XML clause and it is valid only in

SqlCommand object

4. ExecuteXMLReader

ExecuteReader – This method is used when the query will return a

stream of data such as a Select statement. This method returns a set of records that are encapsulated in a SqlDataReader or OleDbDataReader object.

ExecuteScalar – This method is used when the query return a single

value. Usually, this method is used in Select statement returning an aggregate value. The first column of the first row of the result set is the only data that is selected ignoring the other data returned.

ExecuteNonQuery – This method is used when the query will not return a result such as an Insert statement.

ExecuteXMLReader – This method is used when the query includes a

valid FOR XML clause and it is valid only in SqlCommand object. [Executing Commands, Page 10 of 19]

Example of Executing Commands Page 11 of 19

ADO.NET



Imports System



Public Sub Main()



Source=Localhost;Initial Catalog=Pubs;”

Dim conServer As SqlConnection = New

SqlConnection


strConnection

conserver.Open()

Dim commSQL As SqlCommand = New

SqlCommand


commSql.Commandtext = “Select count(*)

from Employees”

‘the code that will query a database and

‘retrieve data

MessageBox.Show(commSql.ExecuteScalar()

.ToString)

End Sub

End Module

Example of Example of Example of Example of Executing CommandsExecuting CommandsExecuting CommandsExecuting Commands

Example of Executing Commands Imports System



Public Sub Main()



Catalog=Pubs;”



conserver.Open()




Employees”

‘the code that will query a database and retrieve

‘data

MessageBox.Show(commSql.ExecuteScalar().ToString)

End Sub

End Module

The code above establishes a connection, creates commands and then

executes the command by using the ExecuteScalar method. A message box is used to display the number of employees. [Example of Executing Commands, Page 11 of 19]

DataReader Object

The DataReader object is used to read a single row of data at a time. There are two versions of this object namely SqlDataReader for SQL Server databases and the OleDbDataReader for other data sources.

To create an instance of the DataReader object, the ExecuteReader



DataReader Object Page 12 of 19

ADO.NET



DataReaderDataReaderDataReaderDataReaderObjectObjectObjectObject

� DataReader object

� used to read a single row of data at a time

• SqlDataReader

• OleDbDataReader

� Create an instance of the DataReader

object:

� ExecuteReader method

� Read method

� Get Method

� Example of Read method

Dim datRead As SqlDataReader = New

SqlDataReader

datRead = commSql.ExecuteReader()

Do Until datRead.Read = False

MessageBox.Show(datRead(1).ToString

& “ “ & datRead(0).ToString)

Loop

datRead.Close()

DataReader Object Page 13 of 19

ADO.NET



DataReaderDataReaderDataReaderDataReaderObjectObjectObjectObject

� Example of Get Method

Dim datRead As SqlDataReader = New

SqlDataReader



MessageBox.Show(datRead.GetString

(1) & “ “ &

datRead.GetString(0))

Loop

method of the Command object can be used. Then, the Read method can be invoked to obtain the data in the rows. The columns in the row can be access by name, ordinal number or native type. An example is shown below to demonstrate how DataReader is used to read a single

row of data at a time. A loop is used to traverse to each row of data. Imports System



Public Sub Main()



Catalog=Pubs;”



conserver.Open()




Employees”

‘the code that will retrieve data by using the

‘DataReader object

Dim datRead As SqlDataReader = New SqlDataReader



MessageBox.Show(datRead(1).ToString & “ “ &

datRead(0).ToString)

Loop

datRead.Close()

End Sub

End Module

The Close method of the DataReader object is called to ensure that

the data stream is closed before accessing any output or return parameters.

Another way of retrieving data in columns is by using the Get methods.

The Get method is used when you know the data types of columns.

This will enhance performance because no type conversion is required.

The code below shows how to use the GetString method to retrieve

data. Dim datRead As SqlDataReader = New SqlDataReader



MessageBox.Show(datRead.GetString(1) & “ “ &

datRead.GetString(0))

Loop

[DataReader Object, Pages 12-13 of 19]



DataAdapter Object Page 14 of 19

ADO.NET



DataAdapterDataAdapterDataAdapterDataAdapterObjectObjectObjectObject

� used to link between data source and

cached tables

� Ways to create a DataAdapter object:

� Using an existing Connection object

� Using a closed connection


ADO.NET




� Example of using an existing Connection objectImports System



Public Sub Main()

Dim strConnection As String = “Integrated Security=True;DataSource=Localhost;InitialCatalog=Books;”



conserver.Open()



commSql.Commandtext = “Select count(*) from Catalogue”

‘the code that will create a DataAdapter

Dim adaptSQL As SqlDataAdapter = New SqlDataAdapter

adaptSQL.SelectCommand = commSQL

End Sub

End Module


ADO.NET




� Example of using a closed connection

Private conServer As

SqlClient.SqlConnection

Public Sub Form1_Load(ByVal sender As

System.Object, ByVal e As

System.EventArgs) Handles MyBase.Load

conserver = New

SqlClient.SqlConnection()




Catalog=Books;”


strConnection

conserver.Open()

End Sub

Private Sub Button1_Click ByVal sender As

System.Object, ByVal e As

System.EventArgs) Handles Button1.Click


Dim adaptSQL As

SqlClient.SqlDataAdapter(“Select

count(*) from Catalogue”, conserver)

End Sub

DataAdapter Object

The DataAdapter object is used to link between data source and cached tables. It is mainly used to retrieve data and insert it into

DataTable objects within a DataSet. A DataSet is a new object for

the caching of data on the client computer. The DataAdapter is also

used to update changes from the DataSet back into the data source. There are two ways to create a DataAdapter object:

1. Using an existing Connection object 2. Using a closed connection

To use an existing Connection object, create a Command object within

a Connection object. Then, assign the SelectCommand property of

the previously instantiated DataAdapter object to that command. An example code is shown below: Imports System



Public Sub Main()



Catalog=Books;”



conserver.Open()




Catalogue”


Dim adaptSQL As SqlDataAdapter = New SqlDataAdapter

adaptSQL.SelectCommand = commSQL

End Sub

End Module

To use a closed connection, instantiate the DataAdapter object

passing a query string and a Connection object. The DataAdapter

will check if the Connection is open. If it is not, the DataAdapter will

open and close it when the method call is complete. Use this method if the Connection object property has been set and need only to open

the connection to populate the data tables. An example code is shown below: Private conServer As SqlClient.SqlConnection

Public Sub Form1_Load(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles MyBase.Load

conserver = New SqlClient.SqlConnection()



Catalog=Books;”


conserver.Open()



End Sub


System.Object, ByVal e As System.EventArgs) Handles

Button1.Click


Dim adaptSQL As SqlClient.SqlDataAdapter(“Select


End Sub

[DataAdapter Object, Pages 14-16 of 19]

Populating the DataTable Page 17 of 19

ADO.NET



Populating the Populating the Populating the Populating the DataTableDataTableDataTableDataTable

� DataTable class

� represents one table of in-memory data

� a central object in the ADO.NET library

� Fill method

� used by passing a DataSet and optionally

the required DataTable as parameters

� used to fill and update multiple DataSets


ADO.NET




� Example of Fill method

Private conServer As

SqlClient.SqlConnection

Public Sub Form1_Load(ByVal sender

As System.Object, ByVal e As

System.EventArgs) Handles

MyBase.Load

conserver = New

SqlClient.SqlConnection()




Catalog=Books;”


strConnection

conserver.Open()

End Sub

Populating the DataTable

The DataTable class represents one table of in-memory data. It is a

central object in the ADO.NET library. DataTable will be discussed

further in the discussion of the DataSet.

The Fill method of the DataAdapter is used by passing a DataSet

and optionally the required DataTable as parameters. It is used to fill

and update multiple DataSets. Once data is acquired, you can work

with the data and if necessary you can use the Update method to synchronize the changes back to the data source. An example is shown below. The code shows how to fill a DataTable.

Note the line of code that invokes the Fill method. It has two

parameters namely the instance of the DataSet and the name of the

DataTable. Private conServer As SqlClient.SqlConnection

Public Sub Form1_Load(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles MyBase.Load

conserver = New SqlClient.SqlConnection()



Catalog=Books;”


conserver.Open()

End Sub


System.Object, ByVal e As System.EventArgs) Handles

Button1.Click

Dim adaptSQL As SqlClient.SqlDataAdapter(“Select


‘the code that will fill the DataSet

Dim datBooks As New DataSet()

adaptSQL.Fill(datBooks, “MyTable”)

‘manipulate data locally using DataSet

adaptSQL.Update(datBooks, “MyTable”)

End Sub

[Populating the DataTable, Pages 17-19 of 19]




ADO.NET




� Example of Fill method (con’t)

Private Sub Button1_Click ByVal

sender As System.Object, ByVal

e As System.EventArgs) Handles

Button1.Click

Dim adaptSQL As

SqlClient.SqlDataAdapter(“Select

count(*) from Catalogue”,

conserver)

‘the code that will fill the

DataSet

Dim datBooks As New DataSet()

adaptSQL.Fill(datBooks,

“MyTable”)

‘manipulate data locally using

DataSet

adaptSQL.Update(datBooks,

“MyTable”)

End Sub

EVALUATION/GENERALIZATION:

• DAO is a set of objects that enables client applications to programmatically access data and is used to access local databases.

• RDO and ADO are new technologies used to access client-server based databases.

• The ADO.NET architecture is divided into two logical entities namely command execution and caching.

• The ADO.Net is the technology used to access data sources.

• There are two namespaces in ADO.Net namely the System,Data.SQLClient and System.Data.OleDb.

• The .NET data providers contain four main objects namely Connection, Command, DataReader and DataAdapter,

• To connect to a database, you perform the following: o Set the connection type. o Specify the data source. o Connect to the data source.

• The Connection object is used to establish database connection.

• The Command object is used to create and execute SQL statement.

• The DataReader object is used to read a single row of data.

• The DataAdapter object is used to link between data source and cached tables.

REFERENCES:

� Microsoft Official Course, (2002), 2373B: Programming with Microsoft Visual Basic .NET, Microsoft Corporation

� Holzner, Steven, (2003), Sams teach yourself Microsoft Visual Basic.Net 2003 in 21 days, USA, Sams Publishing

� Liberty, Jesse, (2003), Learning Visual Basic .NET, USA, O'Reilly & Associates, Inc

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