The ASP.NET page calls these methods, via the data source control, to fetch rows from the database table. Therefore, the next step after deploying the data access class file is to remove the SqlDataSource controls from the page and replace them with instances of the ObjectDataSouce control. Using the Configure Data Source Wizard for each one, you connect these controls to the data access layer so that they can expose the same rowsets as the SqlDataSource controls did. No changes are required to the UI of the page, and - besides the data-access layer class - there is still no code required!

Figure 9 shows the only two steps required to connect the ObjectDataSource that populates the DropDownList of categories to the GetCategoryList method, because this method accepts no parameters. The ObjectDataSource for the GridView control requires a parameter, and this is specified in the third step of the Configure Data Source Wizard - it recognizes that a parameter is required, and you link it up to the SelectedValue property of the DropDownList just as you did when using a SqlDataSource control earlier.

Having added a third ObjectDataSource control to replace the SqlDataSource that populates the DetailsView control, you just connect the DropDownList, GridView, and DetailsView controls to the new data source controls using the tasks panes for each one. Because the data layer does not support editing, the tasks panes do not display the Enable Editing checkbox.

Now you can run the page, and see that - with the exception of editing features - the results are the same . This is just what you want and expect, because the UI has not changed. In addition, the work involved in changing to a data access/business object layer from declarative SQL statements is not difficult or time-consuming.

Caching the Data to Reduce Database Access
It has taken a couple of hours to build the new page for Margaret at AdventureWorks Trading Inc., and you are ready for a break. However, Lucy (the database administrator), has just been told about the new features in the application. It is her job to keep the database running smoothly and efficiently, and she is worried that you are going to slow things down. You are generating constant hits on her database server for every postback as users sort, page, filter, select, and edit rows.

Lucy is a great believer in caching data where it does not change very often, and wants you to implement this in the new page. No, not next week, but now. It looks very much like the game of golf you were planning is not going to happen today.

AdventureWorks Trading Inc. uses the new SQL Server 2005 database, and so you can take advantage of a feature called database cache invalidation to improve performance and reduce database server loading. This makes much more sense than the traditional technique of caching for a specific period, based on a best guess as to how often the data might change.

ASP.NET database cache invalidation supports both SQL Server 2000 and SQL Server 2005. In SQL Server 2000, you use the special tool named aspnet_regsql (in the %windir%\Microsoft.NET\Framework\[version] folder of your machine) to prepare the database and the table containing your source data. You also have to edit your Web.Config file.

In SQL Server 2005, database cache invalidation depends on the Broker Service feature of the database. This allows a SqlCacheDependency to be linked to a data source control so that the data is cached within ASP.NET and only refreshed from the database when it changes (or when another notifiable event such as a server restart occurs on the database server). All that is required, when you use the data source controls, is to add an OutputCache directive to the page that includes a SqlDependency attribute.

<%@OutputCache SqlDependency="CommandNotification"
Duration="60" VaryByParam="*" %>

Note that you must enable the Broker Service for the database, and grant the relevant permissions, before using the Command Notification architecture. For more details, see http://msdn.microsoft.com/library/ enus/dnvs05/html/querynotification.asp.

Now you can run the page and then refresh it without causing a database query to occur (you can monitor database activity using the SQLProfiler tool that comes with SQL Server). However, if you open the source table in Visual Studio or Visual Web Developer and change one of the column values, you will see that the next time you refresh the page there is a hit on the database.

Using a Master Page to Give a Consistent Look and Feel
The styles you applied to the GridView and DetailsView controls, using the Auto Format feature, provide a reasonably attractive outcome. However, they say that beauty is in the eye of the beholder, and so it is no surprise to hear the phone ringing again. This time, Juan-Paul from the marketing department is "just calling to say" that they have a corporate design scheme from their Web site, and he would really appreciate your help to "facilitate an outward appearance of compatibility for reasons of enhanced staff resource utilization via familiarization with the infrastructure."

You take a wild guess that he means he wants the new page to follow the same style and layout as the existing pages. After promising Juan-Paul that you will "personally endeavor to push the envelope, drive the process, and aim skyward toward a satisfactory and visually coherent solution," you fire up Visual Studio again.

Luckily, you took advantage of the Master Pages feature of ASP.NET 2.0 when you built the AdventureWorks Web site. Therefore, fitting the new page into the existing site simply means converting it from a "normal" Web page into a Content Page and referencing the Master Page file. You did this because you realized marketing departments have a changeable attitude to life, and you may well be required to change the whole design and layout of the site at some time in the future. Figure 10 shows the Master Page, with the ContentPlaceHolder control indicating the area occupied by the content from each of the Content Pages. The code that creates this page is shown in Listing 3, where you can see the PlaceHolder control within an HTML table.

All that is required is to strip out of the page all the <html>, <body>, <head>, <form>, and other elements that are not part of the display of rows from the new Web page. Then add the MasterPageFile attribute to the Page directive, and wrap the content in a Content control that specifies the ContentPlaceHolder control on the Master Page that it will populate. Listing 4 shows how this looks in outline.

Now, in Design view of the "product list" page, you can see how the new page fits into the Master Page, with the Master Page itself grayed out and not available for editing unless you open it in a separate window. At runtime, the Master Page content merges into the content generated by the new page you have been building to give the combined result.

Adding a Menu and Other Navigation Features
One item missing from the site is a menu that makes it easy to navigate from one page to another. Again, ASP.NET 2.0 provides all you need to implement various navigation strategies, and the common and effective solution is often a dynamic fly-out or drop-down menu. The data to drive the Menu control comes from an XML file named Web.sitemap, which defines the items for the menu, their position within the hierarchical menu structure, the pop-up tool-tip for each item, and the target URL for navigation. With the new "products" page added to the XML file, the menu will automatically provide a link to this page.

You drag a SiteMapDataSource control from the Toolbox and drop it onto the page, using the Configure Data Source Wizard to select the Web.sitemap file. Then you drag a Menu control from the Toolbox and drop it onto the Master Page, select the new SiteMapDataSource control in the Choose Data Source list, and use the tasks pane to apply a suitable Auto Format.

You also decide to make it easy for users to tell where they are in the site hierarchy by adding a SiteMapPath control to the Master Page as well, at the bottom of the right-hand section of the page below the ContentPlaceHolder control. This uses the same Web.sitemap file, and automatically displays a "breadcrumb trail" for the current page. In addition, like all the other features of ASP.NET 2.0 you have used so far, there is no code to write! It all just works...

Summary
Although this is a somewhat contrived scenario, this excerpt has demonstrated just how powerful ASP.NET 2.0 is, and how it can considerably reduce development time while helping you to construct efficient and attractive Web sites and Web applications. One of the main goals of ASP.NET 2.0 is to reduce even further the amount of code you have to write to build dynamic and interactive pages, removing, in particular, the need for that repetitive code you seem to need for almost all of your projects. As you can see from this excerpt, you can achieve remarkable results without writing any code at all.

You have seen how you can create and then evolve a data access page, starting with dragging a database table onto the editing window. You then saw how easy it is to change the content and appearance of the grid and then add features like sorting, paging, and editing. The next stage added a category selection capability, so that only specific sets of rows appear. Following this was implementation of a "form"-style view of the data. Once the page provided the features required, you next saw how you can make it part of an existing site, by matching the overall style and layout using a Master Page and by integrating it with a menu and navigation system. All this was achieved within the visual design tool, using drag-and-drop techniques and Wizards, and without writing any code at all.

Together, Dave and Al have written many books on Microsoft technologies, including ASP.NET v. 2.0 - The Beta Version (Addison-Wesley, 2005). They are the only two Microsoft "Software Legends' from the UK.