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You can use each SqlDataSource control you create to retrieve a single query. Optionally, you can also add corresponding commands for deleting, inserting, and updating rows. For example, one SqlDataSource is enough to query and update the Customers table in the Northwind database. However, if you need to independently retrieve or update Customers and Orders information, you ll need two SqlDataSource controls. The SqlDataSource command logic is supplied through four properties: SelectCommand, InsertCommand, UpdateCommand, and DeleteCommand, each of which takes a string. The string you supply can be inline SQL (in which case the corresponding SelectCommandType, InsertCommandType, UpdateCommandType, or DeleteCommandType property should be Text, the default) or the name of a stored procedure (in which case the command type is StoredProcedure). You need to define commands only for the types of actions you want to perform. In other words, if you re using a data source for read-only access to a set of records, you need to define only the SelectCommand property.

Protected Sub cmdDisplay_Click(ByVal sender As Object, ByVal e As System.EventArgs) If ViewState("ControlText") IsNot Nothing Then ' Retrieve the hashtable. Dim savedText As Hashtable = CType(ViewState("ControlText"), Hashtable) ' Display all the text by looping through the hashtable. lblResults.Text = String.Empty For Each item As DictionaryEntry In savedText lblResults.Text &= CStr(item.Key) & " = " _ & CStr(item.Value) & "<br />" Next End If End Sub End Class Figure 6-2 shows the result of a simple test, after entering some data, saving it, and retrieving it.

For information about component reuse, see the .NET Components section later in this chapter. For now, you can use the quicker App_Code approach rather than creating a full-fledged, separately compiled component.

If you configure a command in the Properties window, you ll see a property named SelectQuery instead of SelectCommand. The SelectQuery is actually a virtual property that s displayed as a design-time convenience. When you edit the SelectQuery (by clicking the ellipsis next to the property name), you can use a special designer to write the command text (the SelectCommand) and add command parameters (the SelectParameters).

Unlike control properties, member variables that you add to your web-page classes are never saved in view state. Interestingly, you can work around this limitation using view state.

The following OrderService class plays that role. It represents a single <orderService> element and provides access to the three attributes through strongly typed properties: public class OrderService : ConfigurationSection { [ConfigurationProperty("available", IsRequired = false, DefaultValue = true)] public bool Available { get { return (bool)base["available"]; } set { base["available"] = value; } } [ConfigurationProperty("pollTimeout", IsRequired = true)] public TimeSpan PollTimeout { get { return (TimeSpan)base["pollTimeout"]; } set { base["pollTimeout"] = value; } } [ConfigurationProperty("location", IsRequired = true)] public string Location { get { return (string)base["location"]; } set { base["location"] = value; } } }

You have two basic approaches. The first is to create a property procedure that wraps view state access. For example, in the previous web page you could provide the control text hashtable as a property like this: Private Property ControlText() As Hashtable Get If ViewState("ControlText") IsNot Nothing Then Return CType(ViewState("ControlText"), Hashtable) Else Return New Hashtable() End If End Get Set ViewState("ControlText") = Value End Set End Property Now the rest of your page code can freely use the ControlText property, without worrying about how it s being retrieved. The other approach is to save all your member variables to view state when the Page.PreRender event occurs and retrieve them when the Page.Load event occurs. That way, all your other event handlers can use the member variables normally. Keep in mind when you use either of these techniques you must be careful not to store needless amounts of information. If you store unnecessary information in view state, it will enlarge the size of the final page output and can thus slow down page transmission times.

Here s a complete SqlDataSource that defines a SELECT command for retrieving records from the Employees table: <asp:SqlDataSource ID="sourceEmployees" runat="server" ProviderName="System.Data.SqlClient" ConnectionString="<%$ ConnectionStrings:Northwind %>" SelectCommand= "SELECT EmployeeID, FirstName, LastName, Title, City FROM Employees"/>

As you can see, each property is mapped to the corresponding attribute name using the ConfigurationProperty attribute This part is critically important, because it defines the schema (the structure) of your custom section If you add an attribute in your custom section but you don t include a matching ConfigurationProperty attribute, ASPNET will throw an exception when you try to read that part of the webconfig file The ConfigurationProperty attribute also gives you the opportunity to decide whether that piece of information is mandatory and what default value should be used if it isn t supplied In the actual property procedures, the code uses the dictionary of attributes that s provided by the base class You can retrieve the attribute you want from this collection by name Once you ve created the section class, your coding work is complete.