Question

I received the following problem on the MCTS exam. The book says the answer is C, but I thought B would be the correct answer. Why is it C?

You create a new ASP.NET MVC 2 Web application. The following default routes are created in
the Global.asax.cs file. (Line numbers are included for reference only.)

01 public static void RegisterRoutes(RouteCollection routes)
02 {
03 routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
04
05 routes.MapRoute( "Default", "{controller}/{action}/{id}", new { controller = "Home", action = "Index", id = "" } );
06 }

You implement a controller named HomeController that includes methods with the following
signatures.

public ActionResult Index() 
public ActionResult Details(int id) 
public ActionResult DetailsByUsername(string username) 

You need to add a route to meet the following requirements:

• The details for a user must to be displayed when a user name is entered as the path by invoking the DetailsByUsername action.

• User names can contain alphanumeric characters and underscores, and can be between 3 and 20 characters long. What should you do?

A. Replace line 05 with the following code segment.

routes.MapRoute( "Default", "{controller}/{action}/{id}", new { controller = "Home", action = "DetailsByUsername", id = "" } );

B. Replace line 05 with the following code segment.

routes.MapRoute( "Default", "{controller}/{action}/{username}", new { controller = "Home", action = "DetailsByUsername", username = "" }, new { username = @"\w{3,20}" } );

C. At line 04, add the following code segment.

routes.MapRoute( "Details by Username", "{username}", new { controller = "Home", action = "DetailsByUsername" }, new { username = @"\w{3,20}" } );

D. At line 04, add the following code segment.

routes.MapRoute( "Details by Username", "{id}", new { controller = "Home", action = "DetailsByUsername" }, new { id = @"\w{3,20}" } );

Answer 1

When an ASP.NET MVC route looks for an action to map to, it takes several things into account:

1. The action name (Non-case sensitive)
2. The parameter names (non-case sensitive)
3. Whether or not the constraints are matched on the route.

Because of that, if you want a route that matches the criteria you listed, this route would be the correct answer:

routes.MapRoute( 
    "Details by Username", 
    "{username}", 
    new { controller = "Home", action = "DetailsByUsername" }, 
    new { username = @"\w{3,20}" } 
);

A URL with this structure would match that route for the following reasons:

http://example.com/my_user_name

1. The action name matches,
2. It’s looking for a parameter in the action called ‘username’, and
3. The criteria for non-alphanumeric characters is met.

C is the correct answer as it adds to the current routes.

Answer B replaces the existing route definition, thus preventing the default routing to the Home controller Index action.