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ASP.NET calls this method when a request is received. It s where the HTTP handlers perform all the processing. You can access the intrinsic ASP.NET objects (such as Request, Response, and Server) through the HttpContext object that s passed to this method. After ProcessRequest() finishes its work, ASP.NET checks this property to determine whether a given instance of an HTTP handler can be reused. If you return true, the HTTP handler object can be reused for another request of the same type current. If you return false, the HTTP handler object will simply be discarded.

For example, consider an UpdateEmployee stored procedure that takes parameters like this: CREATE PROCEDURE UpdateEmployee @EmployeeID int, @TitleOfCourtesy varchar(25), @Last varchar(20), @First varchar(10) AS ...

All the rich data controls include a DataKeyNames property This property indicates which field (or fields) are considered primary keys To use this feature, you must set the DataKeyNames property with a comma-separated list of one or more key fields Often, you ll have only one key field, as shown here: <asp:GridView ID="gridEmployees" runat="server" DataSourceID="sourceEmployees" DataKeyNames="EmployeeID" .. > Key fields are given special treatment For example, the GridView makes it possible to easily retrieve the key information for a given row Additionally, when you commit an update to a row, the data control passes the original value of the key fields, as well as the changed value (unless it s readonly) The original value is used in a WHERE clause to locate the row so you can perform the update To avoid confusion, the parameter that contains the original value is automatically given the prefix original_.

The following code shows one of the simplest possible HTTP handlers you can create. It simply returns a fixed block of HTML with a message. using System; using System.Web; namespace HttpExtensions { public class SimpleHandler : IHttpHandler { public void ProcessRequest(System.Web.HttpContext context) { HttpResponse response = context.Response;

In this example, the FirstName and LastName fields map to parameters named @First and @Last. Unfortunately, there s no declarative way to correct this problem and map these parameters to their correct names. Instead, you need to define the new parameters and write a little custom code. The first step is to add two parameters to the SqlDataSource.UpdateParameters collection. Unfortunately, you can t create these while the update is in progress. Instead, you need to add them to the SqlDataSource tag: <asp:SqlDataSource ID="sourceEmployees" runat="server" ProviderName="System.Data.SqlClient" ConnectionString="<%$ ConnectionStrings:Northwind %>" SelectCommand= "SELECT EmployeeID, FirstName, LastName, TitleOfCourtesy FROM Employees" UpdateCommand="UpdateEmployee" UpdateCommandType="StoredProcedure" OnUpdating="sourceEmployees_Updating" > <UpdateParameters> <asp:Parameter Name="First" Type="String" /> <asp:Parameter Name="Last" Type="String" /> </UpdateParameters> </asp:SqlDataSource> Note that the parameter names don t include the @ symbol when you define them in the SqlDataSource tag. The next step is to react to the SqlDataSource.Updating event, which fires immediately before the update is committed. You can then set the value for the @First and @Last parameters and remove the @FirstName and @LastName parameters from sight. Here s the code you need: protected void sourceEmployees_Updating(object sender, SqlDataSourceCommandEventArgs e) { e.Command.Parameters["@First"].Value = e.Command.Parameters["@FirstName"].Value; e.Command.Parameters["@Last"].Value = e.Command.Parameters["@LastName"].Value; e.Command.Parameters.Remove(e.Command.Parameters["@FirstName"]); e.Command.Parameters.Remove(e.Command.Parameters["@LastName"]); } This represents a fairly typical scenario in which the no-code data binding won t work. Overall, if you can design your stored procedures and classes to work with the data source controls, you ll avoid writing a great deal of code. On the other hand, if you introduce the data source controls to an existing application with a fixed database schema and database components, it may take a fair bit of extra code to fit these pieces together.

For example, the @EmployeeID parameter becomes @original_EmployeeID This difference can lead to a potential problem You may begin using a parameter name such as @EmployeeID and then set the DataKeyName property to get access to another feature, such as selection When you attempt to perform an update, you ll receive an error indicating the parameter @EmployeeID can t be found What makes this problem even more confusing is that you can take certain actions in Visual Studio such as refreshing the schema for your data control that will automatically set the DataKeyName property without warning you Now that you understand the problem, the solution is quite simple Most of the time you will use the DataKeyNames property, so you should modify your command to use the original value of any read-only primary keys.

response.Write("<html><body><h1>Rendered by the SimpleHandler") ; response.Write("</h1></body></html>") ; } public bool IsReusable { get {return true;} } } }