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Learning ASP.NET 2.0 with AJAX by Dan Hurwitz, Jesse Liberty, Brian MacDonald

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Chapter 4. Saving and Retrieving Data

So far, you've seen how to make good-looking web pages with clever and useful controls. You know how to change the appearance of the page in response to user selections, and how to use AJAX to enhance the performance of your application. But the applications you've made so far have been limited in what they can actually do. In this chapter we add the most frequently sought after functionality: the ability to retrieve, change and store data.

Think about the web sites you visit most often, and you'll find that almost all of them have one thing in common—they interact with persistent data. Persistent data is data that survives a single session; data that you expect will be there the next time you visit. In fact, it may even be data that can have significant financial consequences.

Shopping sites have databases to track their inventories and customer transactions. News sites keep databases with articles and photos in them, perhaps referenced by topic and date. Search engines use unimaginably large (and wicked-fast) databases.

Nearly every real-world commercial web application must be able to perform the four essential "CRUD" interactions with a database: Create, Read, Update, and Delete.

Fortunately, ASP.NET provides controls that make it easy and fast to perform these essential activities. We will demonstrate these interactions with SQL Server Express (or its big brother, SQL Server) but they work equally well—or nearly so—with Microsoft Access and most commercial databases. In theory, you can interact with virtually any collection of data or with XML files, but that is an advanced topic we won't go into here.

Along the way we'll show you enough about database interactions that even if you've never used a relational database, such as SQL Express, you'll have little trouble working with one through your web application.

Getting Data from a Database

To see how to interact with a database, you'll begin by creating a web application that can be used to display information about the AdventureWorks database. You'll start out by simply retrieving and displaying a subset of data. These exercises will teach you how to connect your controls to a database to retrieve, filter, and sort the data and then use the myriad options for presenting it attractively.

As you may remember, AdventureWorks is a free database from Microsoft that represents a fictional company that sells outdoor and extreme sports gear. The database tracks products, inventory, customers, transactions, and suppliers.

Tip

See Chapter 1 for instructions on installing this sample database if you have not already done so.

ASP.NET includes a number of controls specifically designed for displaying data. We'll focus on the GridView control, but other data controls include the DataList, Repeater, DetailsView, and FormView.

The GridView control displays columns and rows of data and allows sorting and paging. It is by far the most popular data display control and is ideal for understanding how data display controls interact with data-retrieval controls and code. The GridView control allows the user to click on a column header to sort the data. GridViews also let you present just a small subset of the data at one time, called a page, with links for easy access to other pages—this process is called "paging" through data. You can do these, and for numerous other data manipulations, with very little programming. A GridView with data from the AdventureWorks database is shown in Figure 4-1.

Binding Data Controls

Database information is stored in memory as tables (just as it is retrieved from a relational database). Tables consist of rows and columns that match nicely to the GridView control.

You could write code to pick out each piece of data you want and write it into the appropriate row or column of the data control, but that's time-consuming and error-prone. It is more efficient and safer to bind the control directly to the underlying data.

Tip

In the early days of Graphical User Interface (GUI) programming, binding was a bit of a "trick"—great for simple programs, but useless for commercial applications because the minute you wanted to do anything out of the ordinary, the binding would become a strait-jacket. Microsoft has solved that with ASP.NET by exposing events on the Data Control that allow you to insert custom code at every stage of the retrieval and binding of the data to the control.

This GridView control displays data from the AdventureWorks database in a table format that makes it easier to read, and allows users to click the column headings to sort the data.

Figure 4-1. This GridView control displays data from the AdventureWorks database in a table format that makes it easier to read, and allows users to click the column headings to sort the data.

Binding is most often used with the larger data controls such as GridView, but you can also bind many other controls, such as DropDownList, ListBox, CheckBoxList, and RadioButtonList. All of these controls have a DataSource property that identifies the source to which the control is bound. For example, you might keep a list of all your customers' names in a database. Binding that data to a ListBox can be a convenient way to allow a customer service representative to quickly pick a customer rather than typing in a name that might otherwise be difficult to spell.

To see how all this works, you'll build the GridView from Figure 4-1. Once you have it up and running, you'll add some features to it, including the ability to use the grid to update the database with new data!

Create a Sample Web Page

To begin, create a new ASP.NET AJAX-enabled web site named AWProductData.

The IDE automatically places the all-important ScriptManager control onto your page. Open your toolbox and click the Data tab. You'll find two types of objects: display controls, which are designed to present data, and DataSource controls, which are designed to help you manage interacting with data sources, as shown in Figure 4-2.

The Data tab in the Toolbox contains the controls that you'll need to display data, and to interact with data sources.

Figure 4-2. The Data tab in the Toolbox contains the controls that you'll need to display data, and to interact with data sources.

Using a DataSource Control

By default, the Data controls are arranged so the display controls are on top, and the DataSource controls are below (You can drag them into any order you like or arrange them alphabetically by right-clicking on any control and selecting Sort Items Alphabetically.) There is a DataSource control for use with Microsoft SQL Server or SQL Server Express, one for Microsoft Access, one for any type of Object, one for use with SiteMaps (for binding to menu controls—more on this in Chapter 6), and one for XML documents as a data source.

Since the AdventureWorks database is a SQL Server database, you'll use the SqlDataSource control whether you are using SQL Server or SQL Server Express. This control will allow you to access the AdventureWorks database, but first you need to direct the control where to find it.

Switch to Design view and drag the SqlDataSource control from the Toolbox directly onto the design surface. A Smart Tag will open, as seen in Figure 4-3.

A Smart Tag opens when you drag the SqlDataSource control onto your page allowing you to configure the data source.

Figure 4-3. A Smart Tag opens when you drag the SqlDataSource control onto your page allowing you to configure the data source.

When you click on Configure Data Source, you invoke a wizard that will walk you through the steps of configuring your data source—hooking up the control to the underlying data table(s).

The first step is to create (or choose) a data connection as seen in Figure 4-4.

To configure your DataSource control, you need to provide it with a data connection. You can choose a preexisting connection from the list (if you have previously created any for this web site), or create a new data connection by clicking the New Connection button.

Figure 4-4. To configure your DataSource control, you need to provide it with a data connection. You can choose a preexisting connection from the list (if you have previously created any for this web site), or create a new data connection by clicking the New Connection button.

Previous data connections in this web site will be listed in the drop-down menu. To make a new connection, click the New Connection… button to get the Add Connection dialog shown in Figure 4-5.

The Add Connection dialog is where you specify a new connection for your data source. Select the server, the logon credentials, and finally the database you want to use.

Figure 4-5. The Add Connection dialog is where you specify a new connection for your data source. Select the server, the logon credentials, and finally the database you want to use.

Following the steps in Figure 4-5, prepare your connection to the database:

  1. Select your server from the Server Name drop-down menu. If it is not there, type the name of the server. Typically, if you are using SQLExpress, the name will be ".\SqlExpress" (dot-slash then SqlExpress) and if you are using SQL Server it will be the name of your computer, or it will be (local)—including the parentheses.

  2. Leave the radio button set to "Use Windows Authentication."

    Tip

    If Windows Authentication does not work, you may need to use SQL Server authentication. If so, your database administrator will tell you what credentials to enter. They may or may not be the same as your Windows login credentials.

  3. Select the option, "Select or enter a database name:".

  4. Choose the AdventureWorks database in the database name drop-down.

  5. Click the Test Connection button to verify that it all works.

This dialog box constructs a connection string, which provides the information necessary to connect to a database on a server.

Click OK to complete the string and return to the Configure Data Source Wizard. Click the plus mark next to "Connection string" to see the connection string you've just created, as shown in Figure 4-6. The segment IntegratedSecurity=True was created when you chose Windows Authentication rather than SQL Server Authentication.

Tip

In Figure 4-6, the Wizard displays an expanded data connection in the drop-down menu, consisting of the name of the server (in this case the local machine, virtdell380, concatenated with sqlexpress, followed by the name of the database and database owner). You don't need to enter this information yourself.

Click the plus sign to view the connection string you just created. This is what gives your control access to the database.

Figure 4-6. Click the plus sign to view the connection string you just created. This is what gives your control access to the database.

When you click Next, the Wizard will ask if you'd like to save this Connection string in the "application configuration file." In an ASP.NET program, the application configuration file is web.config, and saving the connection string there is an excellent idea, so be sure to check the checkbox and give the string a name you can easily remember. The Wizard will make a suggestion for the name of the connection string, as shown in Figure 4-7.

It's a good idea to save the connection string in the application's web.config file, so you can use it again with other controls.

Figure 4-7. It's a good idea to save the connection string in the application's web.config file, so you can use it again with other controls.

This will cause the following lines to be written to web.config:

	<connectionStrings>
	    <add name="AdventureWorksConnectionString"
	         connectionString="Data Source=.\SqlExpress;
	             Initial Catalog=AdventureWorks;Integrated Security=True"
	         providerName="System.Data.SqlClient"/>
	</connectionStrings>

The Wizard next prompts you to configure the SELECT statement. The SELECT statement is the SQL code the control uses to retrieve the exact subset of data you are looking for from the database. Fortunately, if you are not fluent in SQL (most often pronounced "see-quill"), the Wizard will help you build the statement.

Starting with the radio buttons at the top of the dialog box, select "Specify columns from a table or view." (You would select the other button if you had a custom SQL statement prepared, as you'll see shortly.)

Selecting the button, displays the table drop-down menu. Here, you are presented with the various table options that represent the different sets of data in the database. For this exercise, choose the Product table. The various columns from the Product table will be displayed, as shown in Figure 4-8. Simply check the columns you want retrieved, and they'll be added to the SELECT statement. The choices you make will be displayed in the text box at the bottom of the dialog. For this exercise, select the ProductID, Name, ProductNumber, MakeFlag, SafetyStockLevel, and ReorderPoint columns. You could narrow the set of data with the WHERE button, or specify the order in which to retrieve the data with the ORDER BY button. For the moment, you can ignore them both.

To configure the SELECT statement, specify the table and columns within it you want to retrieve, and the Wizard builds the proper SQL statement for you…more or less.

Figure 4-8. To configure the SELECT statement, specify the table and columns within it you want to retrieve, and the Wizard builds the proper SQL statement for you…more or less.

"Pay No Attention to That Man Behind the Curtain"

When you've completed the table setup, click Next, to move to the last page of the Wizard, and then click the Test Query button. The test fails, as shown in Figure 4-9.

The Wizard let you down; the Query Test failed and you're looking at this error message because this database requires a schema name in front of the table names.

Figure 4-9. The Wizard let you down; the Query Test failed and you're looking at this error message because this database requires a schema name in front of the table names.

In this instance, the Wizard falls on its face. It turns out that the AdventureWorks database prefixes a schema name in front of each table name and the Wizard is unprepared for that. It generates a SELECT statement without schema names, as you saw back in Figure 4-8.

Schema in this context refers to an optional name used for organizing the tables in a large database. For example, in the AdventureWorks database, all the tables relating to the HR department have the schema name HumanResources prefixed to every table name, separated by a period, such as HumanResources.EmployeeAddress. Other schemas in the AdventureWorks database include Person, Production, Purchasing, and Sales.

As mentioned, a schema name is optional in SQL. In fact, in our experience, they are rarely used, and the Wizard is unaware of them. However, since the Adventure-Works database (which ships as part of Microsoft SQL Server) does use them, the Wizard becomes confused and flies off to Kansas leaving you on your own.

Tip

The square brackets surrounding each field and table name in the generated SELECT statement are not required, but are used to guarantee that there will be no problems if the name includes any space characters (usually a very bad idea in any case). We often remove them from the finished statement to enhance readability.

Think of this as proof that people are not yet entirely replaceable by automation. Hit the Previous button to go back one step and fix the SELECT statement manually. Click the radio button captioned "Specify a custom SQL statement or stored procedure," and then click Next. In the SQL Statement box, shown in Figure 4-10, type in:

	SELECT ProductID, Name, ProductNumber, MakeFlag, SafetyStockLevel, ReorderPoint
	FROM Production.Product
The SQL statement editing dialog, after adding the schema name to the table name, and removing all the extraneous square brackets.

Figure 4-10. The SQL statement editing dialog, after adding the schema name to the table name, and removing all the extraneous square brackets.

As you can see, this is nearly the same SELECT statement that you built with the Wizard in Figure 4-8, except the Product table now has the required schema (Production) in front of it. We've also left out the square brackets on the columns, as mentioned in the note above.

Click Next to proceed to the next page of the Wizard, and then click Test Query. This time, you should get the results shown in Figure 4-11.

When you test the SELECT statement this time, you'll see the results you were looking for.

Figure 4-11. When you test the SELECT statement this time, you'll see the results you were looking for.

Behold—the triumph of 3 billion years of random mutation and natural selection over 50 years of automation!

Click Finish to save your work. It may not look like much, but you've just enabled your application to access the AdventureWorks database, meaning all that data is now at your control.

Using the GridView Control

Now that the DataSource control is providing the data you want, you need a way to display it. From the Data section of the Toolbox, drag a GridView control onto the page. The GridView control recognizes that a SqlDataSource is on the page and does not create its own.

Tip

If you had dragged the GridView onto the page first, it would have given you the opportunity to create a SqlDataSource rather than assuming you'd like to use one already in existence. It pretty much amounts to the same thing.

Click on the GridView's Smart Tag (if it is not already open). Click the drop-down menu next to "Choose Data Source" and select the DataSource control you just created, as shown in Figure 4-12.

The Smart Tag of the GridView control lets you select the data source you want to use.

Figure 4-12. The Smart Tag of the GridView control lets you select the data source you want to use.

Once the data source is set, the data grid is redrawn, with a column for each field returned by the data source. The column headers are filled in for you based on the column names in the table that the data source represents.

Tip

You'll have an opportunity to make the grid look much prettier, in just a short while.

Open the Smart Tag again and check "Enable Paging," which allows the grid to show a limited number of entries on each page and provide links to the other pages providing access to all the data. Also check "Enable Sorting," which allows the user to sort the grid by clicking on a column header.

Set the page to be the start page for the application (right-click the page in the Solution Explorer and select "Set As Start Page") and then run the application. Figure 4-13 demonstrates how the screen should appear.

Notice that the MakeFlag column (which is a Boolean value of some obscure use to the AdventureWorks business model) is shown as a checkbox. Also note that each of the column headers are shown as links. Click on one of them now—you see that the grid is sorted by that column. Also notice that at the bottom of the grid are links to page through more data, 10 rows at a time. Click on some of those too, to see the various pages.

With the GridView in place and connected to the data source, you can see the data you asked for. Notice the clickable headings and the paging links.

Figure 4-13. With the GridView in place and connected to the data source, you can see the data you asked for. Notice the clickable headings and the paging links.

Each time you click on one of the columns or one of the page numbers the entire page is posted back to the server, and you'll encounter a noticeable delay and flicker. You know how to fix that!

Close the browser and return to Design view. Drag an UpdatePanel control onto the page from the AJAX Extensions section of the Toolbox. Drag both the SqlDataSource and GridView controls already on the page into the UpdatePanel.

Run the application again. Notice there are no visible postbacks when you page or sort, and consequently, no flicker.

Auto-Generated Code

Switch to Source view and look at the markup code that was generated for the GridView. It should appear as highlighted in Example 4-1.

Example 4-1. GridView auto-generated control source code

<%@ Page Language="VB" AutoEventWireup="true" CodeFile="Default.aspx.vb"
Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
        <asp:ScriptManager ID="ScriptManager1" runat="server" />
        <div>
            &nbsp;</div>
        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
            <ContentTemplate>
                <asp:SqlDataSource ID="SqlDataSource1" runat="server"
                   ConnectionString=
                     "<%$ ConnectionStrings:AdventureWorksConnectionString %>"
                     SelectCommand="SELECT [ProductID], [Name],
                     [ProductNumber],
                     [MakeFlag], [SafetyStockLevel], [ReorderPoint]
                     FROM [Production].[Product]" >
                </asp:SqlDataSource>
                <asp:GridView ID="GridView1" runat="server"
                    AllowPaging="True" AllowSorting="True"
                    AutoGenerateColumns="False"
                    DataKeyNames="ProductID" DataSourceID="SqlDataSource1">
                    <Columns>
                        lt;asp:BoundField DataField="ProductID"
                                HeaderText="ProductID" InsertVisible="False"
                                ReadOnly="True"
                                SortExpression="ProductID" />
                        <asp:BoundField DataField="Name" HeaderText="Name"
                                SortExpression="Name" />
                        <asp:BoundField DataField="ProductNumber"
                                HeaderText="ProductNumber"
                                SortExpression="ProductNumber" />
                        <asp:CheckBoxField DataField="MakeFlag"
                                HeaderText="MakeFlag"
                                SortExpression="MakeFlag" />
                        <asp:BoundField DataField="SafetyStockLevel"
                                HeaderText="SafetyStockLevel"
                                SortExpression="SafetyStockLevel" />
                        <asp:BoundField DataField="ReorderPoint"
                                HeaderText="ReorderPoint"
                                SortExpression="ReorderPoint" />
                    </Columns>
                </asp:GridView>
            </ContentTemplate>
        </asp:UpdatePanel>
    </form>
</body>
</html>

The IDE has done a lot of work for you. It has examined the data source and created a BoundField for each column in the data. Further, it has set the HeaderText to the name of the column in the database, represented by the DataField attribute. It has set the AllowPaging and AllowSorting properties to true. In addition, it has also set the SortExpression to the name of the field. Finally, you'll notice on the declaration of the GridView that it has set AutoGenerateColumns to False.

If you were creating the GridView by hand, and if you want to let the grid create all the columns directly from the retrieved data, you could simplify the code by setting AutoGenerateColumns to True. (If AutoGenerateColumns is set to True, and you also include explicitly bound columns, then you will display duplicate data.) To see this at work, create a second GridView by dragging another GridView control from the Toolbox inside the UpdatePanel, below the first.

In the Smart Tag, set the Data Source to the same source as that of the first, SqlDataSource1. Click on the "Enable Paging" and "Enable Sorting" checkboxes.

Now go to Source view. If necessary, delete the <columns> collection from the new grid, GridView2. Change AutoGenerateColumns to the default value: True. The declaration for this second GridView should look something like the following:

	<asp:GridView ID="GridView2" runat="server"
	        AllowPaging="True" AllowSorting="True"
	        DataSourceID="SqlDataSource1" >
	</asp:GridView>

Run the page. Both grids behave identically and are visually indistinguishable. So why does the IDE create the more complex version? By turning off AutoGenerateColumns, the IDE gives you much greater control over the presentation of your data. For example, you can set the headings on the columns (such as changing ProductNumber to Product No.). You can change the order of the columns or remove columns you don't need, and you can add new columns with controls for manipulating the rows.

You can make these changes by manually coding the HTML in the Source view, or by switching to Design View and clicking the Smart Tag for the GridView and choosing Edit Columns. Do that now for GridView1 and you'll see the Fields dialog box, as shown in Figure 4-14.

This dialog box is divided into three main areas: the list of available fields, the list of selected fields (with buttons to remove fields or reorder the list), and the BoundField properties window on the right. When you click on a selected field (such as ProductID), you can set the way that field will be displayed in the data grid (such as changing the header to ID).

While you're examining what you can do with the GridView, let's make it look a little nicer. First, delete or comment out the second (simpler) grid (GridView2) you just created a few moments ago. Second, open the Smart Tag on the original grid. Click AutoFormat and choose one of the formatting options. Of course, you can format it by hand, but why work so hard for a simple example? We'll choose "Brown Sugar" because it shows up well in the printed book. Run the application. The output should appear as in Figure 4-15.

The field editor dialog lets you change the properties of your data columns, without having to do it in Source view.

Figure 4-14. The field editor dialog lets you change the properties of your data columns, without having to do it in Source view.

Adding Insert, Update, and Delete Statements

At this point, the SqlDataSource you've created has only a SELECT statement to extract data from the database:

	SelectCommand="SELECT ProductID, Name, ProductNumber,
	   MakeFlag, SafetyStockLevel, ReorderPoint
	   FROM Production.Product" >

That's fine, if all you want to do is display the data in the database. For a functional site, though, you probably want to be able to add new data, edit existing data, and even delete data. You can do all that just as easily as you did the SELECT statement, by asking your data source control to generate the remaining Create, Retrieve, Update, and Delete statements (fondly known as CRUD statements), using a wizard to make your work easier. To see this in action, switch to Design view, click on the SqlDataSource's Smart Tag, and choose Configure Data Source. The Configure Data Source Wizard opens, displaying your current connection string. Click Next and the Configure Select Statement dialog box is displayed, as shown earlier in Figure 4-8.

The AutoFormat option in the GridView's Smart Tag lets you choose the formatting option that best fits your site, and applies it automatically.

Figure 4-15. The AutoFormat option in the GridView's Smart Tag lets you choose the formatting option that best fits your site, and applies it automatically.

Recall the previous the Configure Data Source Wizard—it did not correctly identify the table in the autogenerated SELECT statement, omitting the schema name. You worked around that by specifying your own SQL statement. Since the SELECT statement you needed was relatively simple to type in, that was not a problem.

However, there is a lot of typing involved for all the CRUD statements. So for the rest of these statements, you will use the Wizard to generate the SQL code, and then just fix the table names.

Make sure the "Specify columns from a table or view" radio button is selected, and the Product table is selected. Check the columns you want returned by the SELECT statement (ProductID, Name, ProductNumber, MakeFlag, SafetyStockLevel, ReorderPoint). This will create a new SELECT statement.

Click the Advanced button to open the Advanced SQL Generation Options dialog box. Select the "Generate INSERT, UPDATE, and DELETE statements" checkbox, as shown in Figure 4-16.

You'll use the Advanced SQL Options dialog box to automatically create the SQL statements to add, edit, and delete data from your data source.

Figure 4-16. You'll use the Advanced SQL Options dialog box to automatically create the SQL statements to add, edit, and delete data from your data source.

Clicking this checkbox instructs the Wizard to create the remaining CRUD statements, and also enables the second checkbox, Use optimistic concurrency. This is a feature that safeguards your data in case another user makes a change to the database at the same time you do. Select this option as well, and Click OK. When you return to the Wizard, click Next then Finish. You may be asked to update your grid, which unfortunately will wipe out all your customization, but the good news is that you are now bound to a data source control that provides all four CRUD methods.

Warning

This Wizard breaks down if any of the fields in the grid can have null values. When a database table is created, you must specify if a column must have data or if null values (no data) are allowed. If you include fields in the GridView which are allowed to be null, then you must handcode the SqlDataSource declaration in Source view.

Open the Smart Tag on the GridView control again, and reapply the look and feel you want. Also—and this is important—select the checkboxes "Enable Editing" and "Enable Deleting."

Switch to Source view. The SqlDataSource markup will appear similar to Example 4-2, except the new SQL commands have been added. You still need to modify the table names, or else you'll get the error you saw earlier (see Figure 4-9). Add the schema name [Production] to each of the four statements highlighted in Example 4-2.

Warning

The following code does not include concurrency detection.

Example 4-2. SqlDataSource with CRUD statements

<asp:SqlDataSource ID="SqlDataSource1" runat="server"
    ConnectionString="<%$ ConnectionStrings:AdventureWorksConnectionString %>"
    SelectCommand=" SELECT [ProductID], [Name], [ProductNumber],
                   [MakeFlag], [SafetyStockLevel], [ReorderPoint]
                   FROM [Production].[Product]"
    DeleteCommand="DELETE FROM [Production].[Product]
                   WHERE [ProductID] = @ProductID"
    InsertCommand="INSERT INTO [Production].[Product] ([Name],
                   [ProductNumber],
                   [MakeFlag], [SafetyStockLevel], [ReorderPoint])
                   VALUES (@Name, @ProductNumber, @MakeFlag,
                   @SafetyStockLevel,
                   @ReorderPoint)"
    UpdateCommand="UPDATE [Production].[Product] SET [Name] = @Name,
                   [ProductNumber] = @ProductNumber,
                   [MakeFlag] = @MakeFlag,
                   [SafetyStockLevel] = @SafetyStockLevel,
                   [ReorderPoint] = @ReorderPoint
                   WHERE [ProductID] = @ProductID" >
    <DeleteParameters>
        <asp:Parameter Name="ProductID" Type="Int32" />
    </DeleteParameters>
    <UpdateParameters>
        <asp:Parameter Name="Name" Type="String" />
        <asp:Parameter Name="ProductNumber" Type="String" />
        <asp:Parameter Name="MakeFlag" Type="Boolean" />
        <asp:Parameter Name="SafetyStockLevel" Type="Int16" />
        <asp:Parameter Name="ReorderPoint" Type="Int16" />
        <asp:Parameter Name="ProductID" Type="Int32" />
    </UpdateParameters>
    <InsertParameters>
        <asp:Parameter Name="Name" Type="String" />
        <asp:Parameter Name="ProductNumber" Type="String" />
        <asp:Parameter Name="MakeFlag" Type="Boolean" />
        <asp:Parameter Name="SafetyStockLevel" Type="Int16" />
        <asp:Parameter Name="ReorderPoint" Type="Int16" />
    </InsertParameters>
</asp:SqlDataSource>

Switch back to Design view and notice the Edit and Delete buttons on each row. They are the result of checking the Enable Editing and Enable Deleting checkboxes.

Taking apart the code in Example 4-2, on the first line is the declaration for the SqlDataSource (and its corresponding closing tag at the bottom). After the ID, the obligatory runat="server", and the ConnectionString attribute, you see four attributes: the SelectCommand (which was there previously) and the new DeleteCommand, InsertCommand, and UpdateCommand.

The DeleteCommand takes a single parameter (@ProductID), which is specified in the DeleteParameters element:

	<DeleteParameters>
	    <asp:Parameter Name="ProductID" Type="Int32" />
	</DeleteParameters>

The UpdateCommand control requires more parameters, one for each column you'll be updating, as well as a parameter for ProductID (to make sure the correct record is updated). Similarly, the InsertCommand takes parameters for each column for the new record. All of these parameters are within the definition of the SqlDataSource.

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