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Commands that compare values are often inefficient, because they require more data to be sent over the network and mean more comparison work for the database. A better solution is to use a timestamp field. If the row is unchanged, the timestamp will always match. In this case, you would hide the timestamp column from the data control but set the DataKeyFields property to include it, so you could use it when constructing your command.

<asp:SqlDataSource ID="sourceEmployees" runat="server" ProviderName="System.Data.SqlClient" ConnectionString="<%$ ConnectionStrings:Northwind %>" SelectCommand="SELECT EmployeeID, FirstName, LastName, Title, City FROM Employees" UpdateCommand="UPDATE Employees SET FirstName=@FirstName, LastName=@LastName, Title=@Title, City=@City FROM Employees WHERE EmployeeID=@EmployeeID"> </asp:SqlDataSource> In this example, the parameter names aren t chosen arbitrarily. As long as you give each parameter the same name as the field it affects and preface it with the @ symbol (so FirstName because @FirstName), you don t need to define the parameter. That s because the ASP.NET data controls automatically submit a collection of parameters with the new values before triggering the update. Each parameter in the collection uses this naming convention. To try this, create a page with the SqlDataSource shown previously and a linked GridView control. Now, take the following steps to enable editing: 1. Select the GridView. In the smart tag, choose the Add New Column link. 2. In the Choose a Field Type box, select CommandField. Then, select the Edit/Update check box and the Show Cancel Button check box. Make sure all other check boxes are unchecked. 3. Click OK to add the column with editing controls. When you complete these steps, the GridView editing controls appear in an additional column. When you run the page and the GridView is bound and displayed, the edit column shows an Edit link next to every record. When clicked, this link switches the corresponding row into edit mode. All fields are changed to text boxes (with the exception of read-only fields), and the Edit link is replaced with an Update link and a Cancel link (see Figure 9-10).

If you want to work at a lower level than the web form model to support a specialized form of processing, you can implement your own HTTP handler. To create a custom HTTP handler, you simply need to author a class that implements the IHttpHandler interface. You can place this class in the App_Code directory, or you can compile it as part of a stand-alone DLL assembly (in other words, a separate class library project). If you use the second approach, you need to add a reference to the project (as described earlier in this chapter). This step instructs Visual Studio to copy the compiled assembly into the Bin directory. The IHttpHandler requires your class to implement two members, which are shown in Table 5-4. Table 5-4. IHttpHandler Members

The update example works just as readily with stored procedures. In this case, you simply supply the stored procedure name for the UpdateCommand: UpdateCommand="UpdateEmployee" UpdateCommandType="StoredProcedure" However, this has a catch. As you ve learned, the parameter names are based on the field names. If the stored procedure uses the same parameter names, the update works without a hitch. However, if the stored procedure parameter names are slightly different, the update will fail.

The Cancel link returns the row to its initial state. The Update link passes the values to the SqlDataSource.UpdateParameters collection (using the field names) and then triggers the SqlDataSource.Update() method to apply the change to the database. Once again, you don t have to write any code. You can create similar parameterized commands for the DeleteCommand and InsertCommand. To enable deleting and inserting, you need to add a column to the GridView that has the ShowInsertButton and ShowDeleteButton properties set to True.

ProcessRequest()

The order of parameters is irrelevant. Only the names are important. The SqlDataSource does a caseinsensitive comparison, so your parameters can have different capitalization.

The GridView is an extremely flexible control. Templates, one of its many features, allow you to define the controls and markup used when editing a record. This is handy if you want to enable editing through drop-down lists, add validation controls, or just fine-tune the appearance of a row in edit mode. You ll learn about templates in 10.