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You can use a similar approach to add extra parameters. For example, if your method requires a parameter with information that s not contained in the linked data control, just define it as one of the UpdateParameters and then set the value when the ObjectDataSource.Updating event fires. If you re more ambitious, you can even decide to programmatically point the ObjectDataSource to a different update method in the same class: sourceEmployees.UpdateMethod = "UpdateEmployeeStrict"; You ll use this approach to solve a common problem in the section The Limits of the Data Source Controls later in this chapter. In fact, to get really adventurous you could set the ConflictDetection property to ConflictOptions.CompareAllValues so that the old and new values are submitted in the UpdateParameters collection. You can then examine these parameters, determine what fields have changed, and call a different method (with different parameters accordingly). Unfortunately, this isn t a zero-code scenario, and you might end up writing some awkward code for updating and removing parameters. Still, it gives you a valuable extra layer of flexibility.

You could take this sorting approach one step further and cascade searches over any arbitrary collection of columns by storing the user s past sort selections in view state and using them to build a larger sort expression. One more technique is available to you. You can sort the GridView programmatically by calling the GridView.Sort() method and supplying a sort expression. This could come in handy if you want to presort a lengthy data report before presenting it to the user. It also makes sense if you want to allow the user to choose from a list of predefined sorting options (listed in another control) rather than use column-header clicks. Figure 10-9 shows an example. When an item is selected from the list, the sort is applied with this code: Protected Sub lstSorts_SelectedIndexChanged( ByVal sender As Object, ByVal e As EventArgs) GridView1.Sort(lstSorts.SelectedValue, SortDirection.Ascending) End Sub

So far, all the examples you ve seen have used parameters to supply values to an update operation. However, you can also create a parameter to return a result. With the SqlDataSource, you can use this option to get access to an output parameter. With the ObjectDataSource, you can use this technique to capture the return value.

// This code tries to match the beginning of the GridView // sort expression The final ASC or DESC part is ignored if (GridView1SortExpressionStartsWith(eSortExpression)) { // This sort is being applied to the same field for the second time // Reverse it if (GridView1SortDirection == SortDirectionAscending) { // This takes care of automatically adding the "DESC" // to the end of the sort expression eSortDirection = SortDirectionDescending; } } } You could use similar logic to turn clicks on different columns into a compound sort For example, you might want to check if the user clicks LastName and then FirstName In this case, you could apply a LastName+FirstName sort protected void GridView1_Sorting(object sender, GridViewSortEventArgs e) { if (eSortExpression == "FirstName" && GridViewSortExpression == "LastName") { // Based on the current sort and the requested sort, a compound // sort makes sense.

All the examples of repeated-value binding that you ve seen so far show all the records of the data source on a single web page. However, this isn t always ideal in real-world situations. Connecting to a data source that contains hundreds or even thousands of records would produce an extremely large page that would take a prohibitively long amount of time to render and transmit to the client browser. Most websites that display data in tables or lists support record pagination, which means showing a fixed number of records per page and providing links to navigate to the previous or next pages to display other records. For example, you have no doubt seen this functionality in search engines that can return thousands of matches.

To see this in action, it s worth considering the InsertEmployee() method, which adds an employee record and returns the newly generated unique ID value as an integer: public int InsertEmployee(EmployeeDetails emp) { ... } You don t need to use the identity value. As you ve seen already, linked data controls are bound after any updates are committed, which ensures that the updated information always appears in the linked controls. However, you might want to use the identity for another purpose, such as displaying a confirmation message. To capture this identity value, you need to define a parameter: <asp:ObjectDataSource ID="sourceEmployees" runat="server" TypeName="DatabaseComponent.EmployeeDB" DataObjectTypeName="DatabaseComponent.EmployeeDetails" SelectMethod="GetEmployees" InsertMethod="InsertEmployee" OnInserted="sourceEmployees_Inserted"> <InsertParameters> <asp:Parameter Direction="ReturnValue" Name="EmployeeID" Type="Int32" /> </InsertParameters> </asp:ObjectDataSource> Now you can retrieve the parameter by responding to the Inserted event, which fires after the insert operation is finished: protected void sourceEmployees_Inserted(object sender, ObjectDataSourceStatusEventArgs e) { if (e.Exception == null) { lblConfirmation.Text = "Inserted record " + e.ReturnValue.ToString(); } }