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Sometimes you ll need to set a parameter with a value that isn t represented by any of the parameter classes in Table 16-1. Or, you might want to manually modify a parameter value before using it. In both of these scenarios, you need to use code to set the parameter value just before the database operation takes place. For example, consider the page shown in Figure 16-13. It includes two data-bound controls. The first is a list of all the customers in the database. Here s the markup that defines the list and its data source: <asp:SqlDataSource ID="sourceCustomers" runat="server" ProviderName="System.Data.SqlClient" ConnectionString="<%$ ConnectionStrings:Northwind %>" SelectCommand="SELECT CustomerID, ContactName FROM Customers" /> <asp:DropDownList ID="lstCustomers" runat="server" DataSourceID="sourceCustomers" DataTextField="ContactName" DataValueField="CustomerID" AutoPostBack="True"> </asp:DropDownList>

Figure 16-13. Using parameters in a master-details page When the user picks a customer from the list, the page is posted back (because AutoPostBack is set to True) and the matching orders are shown in a GridView underneath, using a second data source. This data source pulls the CustomerID for the currently selected customer from the drop-down list using a ControlParameter: <asp:SqlDataSource ID="sourceOrders" runat="server" ProviderName="System.Data.SqlClient" ConnectionString="<%$ ConnectionStrings:Northwind %>" SelectCommand="SELECT OrderID,OrderDate,ShippedDate FROM Orders WHERE CustomerID=@CustomerID"> <SelectParameters> <asp:ControlParameter Name="CustomerID" ControlID="lstCustomers" PropertyName="SelectedValue" /> </SelectParameters> </asp:SqlDataSource> <asp:GridView ID="gridOrders" runat="server" DataSourceID="sourceOrders"> </asp:GridView> Now, imagine you want to limit the order list so it only shows orders made in the last week. This is easy enough to accomplish with a Where clause that examines the OrderDate field. But there s a catch. It doesn t make sense to hard-code the OrderDate value in the query itself, because the range is set based on the current date. And there s no parameter that provides exactly the information you need. The easiest way to solve this problem is to add a new parameter one that you ll be responsible for setting yourself: <asp:SqlDataSource ID="sourceOrders" runat="server" ProviderName="System.Data.SqlClient" ConnectionString="<%$ ConnectionStrings:Northwind %>" SelectCommand="SELECT OrderID,OrderDate,ShippedDate FROM Orders WHERE CustomerID=@CustomerID AND OrderDate>=@EarliestOrderDate" OnSelecting="sourceOrders_Selecting">

Although clicking the Central option forces Solver to make more calculations, it might be useful to Tip

<SelectParameters> <asp:ControlParameter Name="CustomerID" ControlID="lstCustomers" PropertyName="SelectedValue" /> <asp:Parameter Name="EarliestOrderDate" DefaultValue="1900/01/01" /> </SelectParameters> </asp:SqlDataSource> Although you can modify the value of any parameter, if you aren t planning to pull the value out of any of the places listed in Table 16-1, it makes sense to use an ordinary Parameter object, as represented by the <asp:Parameter> element. You can set the data type (if required) and the default value (as demonstrated in this example). Now that you ve created the parameter, you need to set its value before the command takes place. The SqlDataSource has a number of events that are perfect for setting parameter values. You can fill in parameters for a select operation by reacting to the Selecting event. Similarly, you can use the Updating, Deleting, and Inserting events when updating, deleting, or inserting a record. In these event handlers, you can access the command that s about to be executed through the SqlDataSourceSelectingEventArgs.Command property, and modify its parameter values by hand. (The SqlCommand also provides similarly named Selected, Updated, Deleted, and Inserted events, but these take place after the operation has been completed, so it s too late to change the parameter value.) Here s the code that s needed to set the parameter value to a date that s seven days in the past, ensuring you see one week s worth of records: Protected Sub sourceOrders_Selecting(ByVal sender As Object, _ ByVal e As SqlDataSourceSelectingEventArgs) Handles sourceOrders.Selecting e.Command.Parameters("@EarliestOrderDate").Value = _ DateTime.Today.AddDays(-7) End Sub

Listing 11-4. The app/views/users/login.ctp File 1 2 3 4 5 6 <h1>Log In</h1> < if ($session->check('Message.auth')) $session->flash('auth'); > < =$form->create('User',array('action'=>'login')); > < =$form->input('username'); > < =$form->input('password',array('type'=>'password')); > < =$form->end('Login'); >

Note You ll have to tweak this code slightly if you re using it with the standard Northwind database. The

data in the Northwind database is historical, and most orders bear dates around 1997. As a result, the previous code won t actually retrieve any records. But if you use the AddYears() method instead of AddDays(), you can easily move back ten years to the place you need to be.