Walkthrough: Retrieving, Updating, Inserting, and Deleting Data with the LinqDataSource and DetailsView Controls

Artykuł
11/16/2012

In this walkthrough, you will create a simple database table and a Web page that uses the LinqDataSource control. The Web page enables users to retrieve, update, insert, and delete data from the database table. You will use a DetailsView control to display the data. The LinqDataSource control enables you to perform all these operations without writing Select, Update, Insert, or Delete statements.

You will use the Object Relational Designer to create a class that represents the database table that contains the values. The LinqDataSource control will interact with this generated class to retrieve, update, insert and delete the data.

Prerequisites

To implement the procedures in your own development environment you need:

Visual Studio 2008 or Visual Web Developer Express.
SQL Server Express Edition installed on your computer. If you have SQL Server installed, you can use that instead, but you must make small adjustments to some of the procedures.
An ASP.NET Web site.

Creating a Database Table

To perform the steps in this walkthrough, you must have a database table. If you do not already have a table, you can create one by using the following procedure. If you use an existing table, the steps in some of the procedures will not match your database exactly. However, the concepts illustrated in the walkthrough will be the same.

To create a database table

If the Web site does not already have an App_Data folder, in Solution Explorer, right-click the project, click Add ASP.NET Folder, and then click App_Data.
Right click the App_Data folder and then click Add New Item.
Under Installed Templates, select SQL Database, change the file name to Reviews.mdf, and then click Add.
In Server Explorer, open the Reviews.mdf node and then right-click the Tables folder.
Click Add New Table.
Create the following columns in the table:

Column Name

Data Type

Properties

MovieID

int

IsIdentity = Yes

Not null

Primary Key

Title

nvarchar(50)

Theater

nvarchar(50)

Review

nvarchar(1000)

Score

int

Not null
Save the table and name it MovieReviews.
In Server Explorer, right-click the MovieReviews table and click Show Table Data.
Manually add values for the fields. You do not have to specify a value for MovieID because that value is generated by the database.

Column Name	Data Type	Properties
MovieID	int	IsIdentity = Yes Not null Primary Key
Title	nvarchar(50)
Theater	nvarchar(50)
Review	nvarchar(1000)
Score	int	Not null

Creating Classes to Represent Database Entities

To work with the LinqDataSource control, you work with classes that represent database entities. You can use a tool in Visual Studio 2008 or Visual Web Developer Express to create these classes.

To create a class for the MovieReviews table

If the Web site does not already have an App_Code folder, in Solution Explorer, right-click the project, click Add ASP.NET Folder, and then click App_Code.
Right-click the App_Code folder and then click Add New Item.
Under Installed templates, select Linq to SQL Classes template, rename the file Reviews.dbml, and then click Add.

The Object Relational Designer is displayed.
In Server Explorer, drag the MovieReviews table into the Object Relational Designer window.

The MovieReviews table and its columns are represented as an entity named MovieReview in the designer window.
Save the Reviews.dbml file.
In Solution Explorer, open the Reviews.designer.cs or Reviews.designer.vb file.

Notice that it now has classes for ReviewsDataContext and MovieReview. The ReviewsDataContext class represents the database and the MovieReview class represents the database table. The parameterless constructor for the ReviewsDataContext class reads the connection string from the Web.config file.
Open the Web.config file.

Notice that the connection string has been added in the connectionStrings element.
Close the class file and the Web.config file.

Creating and Configuring a LinqDataSource Control

Now that you have a database table and classes that represent database entities, you can use a LinqDataSource control on an ASP.NET Web page to manage data.

To create and configure a LinqDataSource control

In Visual Studio, create a new ASP.NET Web page and switch to Design view.
From the Data tab of the Toolbox, drag a LinqDataSource control and drop it inside the form element on the Web page.

You can leave the ID property as LinqDataSource1.
In the Smart Tag panel, click Configure Data Source.
In the Configure Data Source dialog box, select ReviewsDataContext.
Set the TableName property to "MovieReviews".

The following example shows the markup for the LinqDataSource control.
```
<asp:LinqDataSource 
  ContextTypeName="ReviewsDataContext" 
  TableName="MovieReviews" 
  ID="LinqDataSource1" 
  runat="server">
</asp:LinqDataSource>
```
Notice that you did not have to specify any database commands for selecting the data.

Adding a Control to Display Data

You can now add a DetailsView control and bind it to the LinqDataSource control. The DetailsView control enables users to view data that is managed by the LinqDataSource control.

To connect the data from the LinqDataSource to a DetailsView

Switch to Design view.
From the Data tab of the Toolbox, drag a DetailsView control onto the page.

You can leave the ID property as DetailsView1.
In the Smart Tag panel, set the data source to LinqDataSource1.

Select the Enable Paging option.

The following example shows the markup for the DetailsView control. Notice that the DataKeyNames property was automatically set to the primary key field in the table, and that a bound field was added for each field in the table.

<asp:DetailsView 
  DataSourceID="LinqDataSource1" 
  DataKeyNames="MovieID" 
  AllowPaging="true" 
  AutoGenerateRows="False"
  ID="DetailsView1" 
  runat="server"
  Height="50px"
  Width="125px">
  <Fields>
    <asp:BoundField 
         DataField="MovieID" 
         HeaderText="MovieID" 
         InsertVisible="False" 
         ReadOnly="True" 
         SortExpression="MovieID" />
    <asp:BoundField 
         DataField="Title" 
         HeaderText="Title" 
         SortExpression="Title" />
    <asp:BoundField 
         DataField="Theater" 
         HeaderText="Theater" 
         SortExpression="Theater" />
    <asp:BoundField 
         DataField="Review" 
         HeaderText="Review" 
         SortExpression="Review" />
    <asp:BoundField 
         DataField="Score" 
         HeaderText="Score" 
         SortExpression="Score" />
  </Fields>
</asp:DetailsView>

Save the changes and then press CTRL+F5 to view the page in a browser.

The DetailsView control displays the values for the current record from the MovieReviews table.

Enabling Users to Update, Insert, and Delete Data

The LinqDataSource control can create the commands for updating, inserting, and deleting data.

To enable update, insert, and delete operations

In the LinqDataSource control, select the Enable Delete, Enable Insert, and Enable Update options.

Enable update, insert and delete.

The following example shows the declarative markup for the LinqDataSource control.

<asp:LinqDataSource 
  ContextTypeName="ReviewsDataContext" 
  TableName="MovieReviews" 
  EnableUpdate="true" 
  EnableInsert="true" 
  EnableDelete="true" 
  ID="LinqDataSource1" 
  runat="server">
</asp:LinqDataSource>

In the DetailsView control, select the Enable Inserting, Enable Editing, and Enable Deleting options.

Enable inserting, updating and deleting.

The following example shows the declarative markup for the DetailsView control.

<asp:DetailsView 
  DataSourceID="LinqDataSource1" 
  DataKeyNames="MovieID" 
  AutoGenerateRows="false" 
  AllowPaging="true" 
  ID="DetailsView1" 
  runat="server"
  Height="50px" 
  Width="125px">
  <Fields>
    <asp:BoundField 
         DataField="MovieID" 
         HeaderText="MovieID" 
         InsertVisible="False" 
         ReadOnly="True" 
         SortExpression="MovieID" />
    <asp:BoundField 
         DataField="Title" 
         HeaderText="Title" 
         SortExpression="Title" />
    <asp:BoundField 
         DataField="Theater" 
         HeaderText="Theater" 
         SortExpression="Theater" />
    <asp:BoundField 
         DataField="Review" 
         HeaderText="Review" 
         SortExpression="Review" />
    <asp:BoundField 
         DataField="Score" 
         HeaderText="Score" 
         SortExpression="Score" />
    <asp:CommandField 
         ShowDeleteButton="True" 
         ShowEditButton="True" 
         ShowInsertButton="True" />
  </Fields>
</asp:DetailsView>

The MovieID column is selected from the data source with the other columns. However, it is not displayed in the DetailsView control and the user will not be able to modify its value. The MovieID property must be selected to enable the LinqDataSource control to automatically create the commands for updating, inserting, and deleting data.

Notice that you did not have to specify commands for these data operations.

Save the changes and press CTRL+F5 to view the page in a browser.

The DetailsView control displays the fields for the current record from the MovieReviews table. You can update, insert, and delete records by clicking the corresponding buttons on the DetailsView control.

Next Steps

This walkthrough has shown the basic functionality of updating, inserting, and deleting records by using the LinqDataSource control. To learn about additional capabilities of the LinqDataSource control, you can do the following:

You can filter which data records are returned by specifying a value for the Where property. You can also select only a subset of columns by specifying a value for the Select property. For more information, see Walkthrough: Selecting and Filtering a Subset of Data with the LinqDataSource and GridView Controls.
To make sure that the data in the database has not changed since the Web page read it, the LinqDataSource controls stores the original values of all the selected data. When the update is posted to the Web server, the LinqDataSource object compares each stored field with the current value in the database. If they match (indicating that the record has not changed), the LinqDataSource object updates or deletes the record. Storing all the original column values can be inefficient. To avoid this issue, you can add a timestamp column to your database table. For more information, see Walkthrough: Using a Timestamp with the LinqDataSource Control to Check Data Integrity.

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