ado.net session07

of 23Ver. 1.0

Developing Database Applications Using ADO.NET and XML

Session 7

In this session, you will learn to:Working in a disconnected environment

Objectives

of 23Ver. 1.0


Session 7

In a disconnected environment, data is stored in datasets and manipulations are performed in the datasets. After the data has been manipulated in the dataset, the changes are updated to the database. A dataset is a disconnected, cached set of records that are retrieved from a database. The dataset acts like a virtual database containing tables, rows, and columns.The two main types of datasets are:

Typed datasetUntyped dataset

Let us discuss each of these types in detail.

Working with Datasets and Datatables

of 23Ver. 1.0


Session 7

Typed Dataset:A typed dataset is derived from the DataSet class and has an associated XML schema, which is created at the time of creation of the dataset. The XML schema contains information about the dataset structure such as the tables, columns, and rows.The XML Schema Definition (XSD) language is used to define the elements and attributes of XML documents.The structure of a typed dataset is decided at the time of its creation.When a typed dataset is created, the data commands are generated automatically by using the column names from the data source.

Working with Datasets and Datatables (Contd.)

of 23Ver. 1.0


Session 7

Untyped Dataset:An untyped dataset does not have any associated XML schema. In an untyped dataset, the tables and columns are represented as collections. Because an XML schema is not created for an untyped dataset, the structure of an untyped dataset is not known during compilation. Untyped datasets find their use in cases where the structure of the schema is not decided during compilation or the data being used does not have a definite structure.


of 23Ver. 1.0


Session 7

A dataset has its own object model, as shown in the following figure.


of 23Ver. 1.0


Session 7

A dataset is created with the help of a DataSet object.The DataSet object is present in a DataSet class and is defined in the System.Data namespace. The DataSet object contains a collection of DataTable objects, each containing one or more tables. A DataTable object contains one or more columns, each represented by a DataColumn object. To add a column to a DataTable, create a DataColumn object and call the Add() method on the Columns collection, which enables you to access the columns in a datatable.


of 23Ver. 1.0


Session 7

The following list describes some parameters that can be specified for a column:

The name of the columnThe data type of the columnWhether the column is read onlyWhether the column permits null valuesWhether the value of the column must be different in each rowWhether the column is an auto-increment columnWhether the column is an expression column


of 23Ver. 1.0


Session 7

Consider the following code snippet used for adding columns in a DataTable: DataSet ds = new DataSet();DataTable dt = ds.Tables.Add();dt.Columns.Add(“Store Id”, typeof(string));dt.Columns.Add(“Store Name”, typeof(string));dt.Columns.Add(“Address”, typeof(string));

Creating a DataSet object Creating a DataTable objectAdding columns in a DataTable


of 23Ver. 1.0


Session 7

A DataTable object also has a Rows collection that allows rows to be accessed in a dataset. The various methods performed on a row by using the DataRow object are:

Add()InsertAt()Find()Select()Remove()RemoveAt()Delete() Removes a row provisionally from a table

Appends the row to the end of the table

Inserts the row at a specified position

Accesses a row in a table by its primary key value

Finds rows that match a specified condition

Removes the specified DataRow object

Removes the row at a specified position


of 23Ver. 1.0


Session 7

Which method of the DataRow object accesses a row in a table by its primary key value?1. Find()2. Select()3. InsertAt()4. Add()

Just a minute

Answer:1. Find()

of 23Ver. 1.0


Session 7

In ADO.NET, you can navigate through multiple tables to validate and summarize the data by using the DataRelation object.By using primary key and foreign key constraints that use a DataRelation object, you can create the relationship between multiple tables.The primary key is a unique index and ensures the uniqueness of data stored in that table for that particular row.The foreign key is a constraint on a table that can reference one or more columns in that table.The table that has a primary key constraint is known as the Parent table, and the table that has a foreign key constraint is known as the Child table.


of 23Ver. 1.0


Session 7

A DataSet.Relations property gets the collection of relations that link tables and allow navigation from Parent tables to Child tables. The Rule enumeration indicates the action that occurs when a foreign key constraint is enforced. The various Rule enumeration values are:

Cascade

None

SetDefault

SetNull

Deletes or updates the child DataRow object when the parent DataRow object is deleted or its unique key is changed

Throws an exception if the parent DataRow object is deleted or its unique key is changed

Sets the foreign key column(s) value to the default value of the DataColumn object(s), if the parent DataRow object is deleted or its unique key is changedSets the foreign key column(s) value to DbNull, if the parent DataRow object is deleted or its unique key is changed


of 23Ver. 1.0


Session 7

Sometimes, the data available in one DataSet can be merged with another DataSet. Or, a copy of the DataTable objects can be created so that the user can edit or modify data, which can then be merged back to the original dataset. The Merge() method is used to combine data from multiple DataSet, DataTable, and DataRow objects.During merging of data within datasets, the MissingSchemaAction enumeration specifies the action to be taken when the data added to the dataset and the required DataTable or DataColumn is missing.


of 23Ver. 1.0


Session 7

The various values of MissingSchemaAction enumeration are:

Add

AddWithPrimaryKey

Error

Ignore

Adds the DataTable and DataColumn objects to complete the schema

Adds the DataTable, DataColumn, and PrimaryKey objects to complete the schema Throws an exception if the DataColumn does not exist in the DataSet that is being updated Ignores data that resides in DataColumns that are not in the DataSet being updated


of 23Ver. 1.0


Session 7

A dataview provides a dynamic view of data stored in a datatable. If any data is modified in the datatable, the dataview associated with the datatable will also show the modified data.Let us understand the object model of a dataview.

Working with Dataviews

of 23Ver. 1.0


Session 7

The following figure shows the object model of a dataview.

Working with Dataviews (Contd.)

DataSet Object

DataTable Object

DataView Objects

Alternative Sort/Filter Criteria

Additional Views

DataView Object

Default Sort/Filter Criteria

DefaultView

of 23Ver. 1.0


Session 7

A DataView object creates a fixed customized view of a given DataTable object.You can create a DataView object to display the data based on a criterion and another DataView object to display the data based on a different criterion.The following figure shows how customized data is displayed through dataviews.

Windows Application

DataView1

DataView2

DataView3

Filter3

Filter2

Filter1

DataTable


of 23Ver. 1.0


Session 7

A dataview provides a sorted or filtered view of data in a datatable. Sorting in a DataTable by using a DataView object is done by using the Sort property. Filtering a DataTable by using the DataView object is done by using the RowFilter and RowStateFilter properties.


of 23Ver. 1.0


Session 7

Which property of the DataView object returns a subset of rows on the basis of the column values?1. FindRows2. RowFilter3. RowStateFilter4. Find

Just a minute

Answer:2. RowFilter

of 23Ver. 1.0


Session 7

Problem Statement:Jane, a member of the HR team at Tebisco, needs to store the details of employees who have recently joined the organization. You need to create an application for Jane that will enable her to add and save the details of new employees, and if required, delete records of employees who are no longer working in the organization. The employee code should get automatically generated based on the format in the table. The employee details will be stored in the empdetails table of the HR database.

Demo: Manipulating Data in a Disconnected Environment

of 23Ver. 1.0


Session 7

In this session, you learned that: A dataset, which is a part of disconnected environment, is a disconnected, cached set of records that are retrieved from a database. The two main types of datasets are:

Typed datasetsUntyped datasets

A typed dataset is derived from the DataSet class and has an associated XML schema, which is created at the time of creation of a dataset.An untyped dataset does not have any associated XML schema. As a result, the structure of an untyped dataset is not known during compilation.

Summary

of 23Ver. 1.0


Session 7

The DataSet object contains a collection of DataTable objects, each containing one or more tables.A DataTable object contains one or more columns, each represented by a DataColumn object.A DataTable object also has a Rows collection, which allows rows to be accessed in a dataset. A DataTable object contains one or more rows, each represented by a DataRow object.The DataRelation object is used to navigate through multiple tables to validate and summarize the data.The primary key and foreign key constraints in a DataRelation object create the relationship between the tables in a schema.

Summary (Contd.)

of 23Ver. 1.0


Session 7

The Merge() method is used to combine data from multiple DataSet, DataTable, and DataRow objects. A dataview, which is a part of the disconnected environment, enables you to create a dynamic view of data stored in a datatable. A DataTable can have multiple DataView objects assigned to it, allowing the data to be viewed in different ways without having to re-read from the database.Sorting in a DataTable by using the DataView object is done by using the Sort property.Filtering in DataTable using DataView object is done by using the RowFilter and RowStateFilter properties.

Summary (Contd.)

ado.net session07

Technology