Question

I recently got burned by the fact that these two MVC4 routes, apparently, function differently. I was wondering if someone could highlight what’s going on so I could better understand.

routes.MapRoute(
    "post-User",
    "User",
    new { controller = "User", action = "create" },
    new { httpMethod = new HttpMethodConstraint("POST") }
    );

routes.MapRoute(
    "post-User",
    "{controller}",
    new { controller = "User", action = "create" },
    new { httpMethod = new HttpMethodConstraint("POST") }
    );

I thought that the {controller} bit was a placeholder and that saying controller = “User” in the next line would make these two statements equivilant. Apparently using {controller} sets up defaults for all routes?

Answer 1

You are correct in your belief that the {controller} substring acts as a placeholder for a controller name. With that in mind, then, the following route will match any controller, but default to the User controller where no controller is specified:

routes.MapRoute(
    "post-User",
    "{controller}",
    new { controller = "User", action = "create" },
    new { httpMethod = new HttpMethodConstraint("POST") }
);

The following, however, will match the route User and – because no controller can be specified – will always route to the User controller:

routes.MapRoute(
    "post-User",
    "User",
    new { controller = "User", action = "create" },
    new { httpMethod = new HttpMethodConstraint("POST") }
);

In this instance the difference is meaningless because all you’re doing is forcing the route User to map to a controller User, which is exactly what will happen in your first route anyway.

However, consider the following:

routes.MapRoute(
    "post-User",
    "User/{action}",
    new { controller = "User", action = "MyDefaultAction" },
    new { httpMethod = new HttpMethodConstraint("POST") }
);

routes.MapRoute(
    "foo",
    "{controller}/{action}",
    new { controller = "User", action = "Index" },
    new { httpMethod = new HttpMethodConstraint("POST") }
);

Now, your top route will match requests to the User controller, with an optional action specified and will default to MyDefaultAction. Requests to any other controller will not match the first route – because the route does not begin with the constant string User – and will default back to the second route (foo). Again, the action is optional; however, now, unlike the requests to the User controller, your default action for other controllers will be the Index action.

So now…

.../User defaults to the MyDefaultAction action.

.../SomeOtherController defaults to the Index action.