MSDN Magazine - October 2007 - (Page 43)

AJAX Application Architecture, Part 2 DINO ESPOSITO W hen using ASP.NET AJAX Extensions to tranof this work without writing any code. For a successFront End with JavaScript sition your site to an AJAX experience, there ful login to take place, though, there is a redirection are two main programming models to choose from: (HTTP 302) when the user hits a protected page, a JSON objects partial rendering and script services. In last month’s postback from the login page to authenticate crecolumn, I discussed partial rendering from a primardentials, and then another redirection back to the Back End with Services ily architectural perspective. Simply put, with partial originally requested page. rendering, you don’t need to change the underlying This isn’t necessarily the case with AJAX pages. If Other Back-End Tiers architecture of an ASP.NET application—it’s an easy the user requests a protected page from the address route to implementing some of the best elements of Figure 1 Typical AJAX bar, there’s not much you can do other than repeatAJAX, such as no-flicker updates to pages on your Architecture ing the ASP.NET experience. If, however, you have site. This enhanced behavior is achieved by simlinks in your page that point to protected pages, ply adding a few new server controls (specifically, ScriptManager you can add some script to the onclick event of the link to check and UpdatePanel) and having them silently perform a few tricks whether the user is authenticated. If not, you can then pop up an to transform a traditional postback in an asynchronous request alert box to warn the user, like this: function checkFirst() run through the XMLHttpRequest object. This approach is pret{ ty easy as it simply applies AJAX functionality to the existing Web var loggedIn = Sys.Services.AuthenticationService.get_isLoggedIn(); if (!loggedIn) development model. { If you’re ready for a full paradigm shift in building AJAX applialert(“You must be logged in to follow this link”); return false; cations, then you should be looking at the script services approach. } All in all, the typical AJAX architecture is fairly easy to understand. return true; } Figure 1 illustrates a high-level view of how it works. There’s a back end made of application-specific services, which are usually just an As you can see, this approach uses a client framework that, AJAX script-callable façade on top of the middle tier of the system among other things, allows you to check whether the current user where the business logic lives and works. Services and the front end is logged in. With ASP.NET AJAX Extensions, you do that through exchange data via HTTP using a variety of formats to pass param- the Sys.Services.AuthenticationService class. eters and return values. After receiving and processing data, the The same service can be used to authenticate a user after she front end, which is made of JavaScript code running on the client, specifies valid credentials. In this case, there is no redirection and faces the nontrivial task of building a graphical UI using HTML no postback. Everything happens in the context of the same page, and JavaScript. The reliance on JavaScript is a structural constraint as the following code snippet demonstrates: of the browser and this will only change once the browser can supfunction OnLogin() { port more powerful programming capabilities. Sys.Services.AuthenticationService.login( Logging In with AJAX Moving away from the classic ASP.NET model has numerous practical repercussions. Consider the login process and see how it would change in a pure AJAX solution. Currently with ASP.NET, enabling the login process consists of configuring the login page with the Login control, configuring protected pages with the LoginView control, and setting up the ASP.NET membership provider. Protected pages will use either logged-in or anonymous templates to reflect the result of the authentication process graphically. In ASP.NET 2.0, you can do most } $get(“UserName”).value, $get(“Password”).value, false, null, null, OnLoginCompleted, OnLoginFailed); Checking credentials becomes a standard script operation that uses a script service to authenticate. It’s up to the developer to update the client page’s UI to reflect that the user is logged in once authentication succeeds. Unless the framework you use provides an object model to wrap HTML in controls, you have to take the october2007 43

Table of Contents Feed for the Digital Edition of MSDN Magazine - October 2007

Cover Contents Toolbox CLR Inside Out Basic Instincts Data Points Cutting Edge Pooled Threads WPF Threads Parallel Linq Parallel Performance Mobile Apps Test Run Foundations Windows with C++ Netting C++ .NET Matters { End Bracket } Net Nuptials

MSDN Magazine - October 2007

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