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The ObjectDataSource allows you to create a declarative link between your web-page controls and a data access component that queries and updates data. The ObjectDataSource is remarkably flexible and can work with a variety of different components. However, to use it, your data access class must conform to a few rules: It must be stateless. That s because the ObjectDataSource will create an instance only when needed and destroy it at the end of every request. It must have a default, no-argument constructor. All the logic must be contained in a single class. (If you want to use different classes for selecting and updating your data, you ll need to wrap them in another higher-level class.) None of the linked methods (for selecting or updating records) can be static. It must provide the query results when a single method is called. The query results are several records, which can be represented as a collection, an array, or a list object that implements IEnumerable. Each record should be a custom object that exposes all its data through public properties. You can work around many of these rules by handling ObjectDataSource events and writing custom code. However, if you want your data access class to plug into the data-binding model seamlessly without extra work, you should observe these guidelines.

if (line != null) { // Make sure tags and other special characters are // replaced by their corresponding HTML entities so that // they can be displayed appropriately. line = server.HtmlEncode(line); // Replace spaces and tabs with nonbreaking spaces // to preserve whitespace. line = line.Replace(" ", " "); line = line.Replace( "\t", "     "); // A more sophisticated source viewer might apply // color coding. response.Write(line + "<br />"); } } r.Close(); } catch (Exception err) { response.Write(err.Message); } response.Write("</html></body>"); } public bool IsReusable { get {return true;} } } } This code simply finds the requested file, reads its content, and uses a little string substitution (for example, replacing spaces with nonbreaking spaces and line breaks with the <br /> element) and HTML encoding to create a representation that can be safely displayed in a browser. You ll learn more about techniques for reading and manipulating files in 13. Next, you can map the handler to a file extension, as follows: <httpHandlers> <add verb="*" path="source.simple" type="HttpExtensions.SourceHandler,HttpExtensions"/> </httpHandlers> To test this handler, you can use a URL in this format: http://localhost:[Port]/05/source.simple file=HolmesQuote.aspx.cs The HTTP handler will then show the source code for the .cs file, as shown in Figure 5-14.

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 ... 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.

For example, consider the data-bound page in Figure 9-8. You can create the same page using the custom data access component developed in 8. You can refer to 8 to see the full code, which has the following structure: public class EmployeeDB { public int InsertEmployee(EmployeeDetails emp) { ... } public void DeleteEmployee(int employeeID) { ... } public EmployeeDetails GetEmployee() { ... } public EmployeeDetails[] GetEmployees() { ... } public int CountEmployees() { ... } } The first step to use this class in your page is to define the ObjectDataSource and indicate the name of the class that contains the data access methods. You do this by specifying the fully qualified class name with the TypeName property: <asp:ObjectDataSource ID="ObjectDataSource1" runat="server" TypeName="DatabaseComponent.EmployeeDB" ... />