Improving Asp.net MVC maintainability and RESTful conformance

I've used Asp.net MVC for a few years now but this issue I've stumbled upon just a few days ago seems something everydayish and I wonder how come I've never bumped into it. It has to do with Asp.net MVC routing and action method selection. First of all think of default route definition that looks like this:

   1:  // default application route

   2:  routes.MapRoute(

   3:      "Default",

   4:      "{controller}/{action}/{id}",

   5:      new { controller = "Home", action = "Index", id = UrlParameter.Optional }

   6:  );

Mind that id route value is optional? Yes optional. So it should be perfectly feasible to have two action methods: one with the id parameter and one without it: public ActionResult Index() { ... } and public ActionResult Index(int id) { ... } But you've probably guessed it? This doesn't work out of the box. You'll get a runtime error stating that there are two matching action methods for the current request. A bit strange? I thought so as well. So let's try and accomplish just that!

Custom action method selector attributes in Asp.net MVC

Some of the least customized but very useful extension points in Asp.net MVC are action method selector attributes. We use them all the time without actually knowing, but we may write our own as well and make seemingly complex things trivial.

A real world example

Take for instance Twitter website. When you first visit their site, you are presented with the anonymous visitor home page that provides search capabilities, trends etc.

But when you're logged in you see a completely different page. Web address is still the same, but content is completely different. You see your home twitter page where you can send tweets and read your stream.

Using custom action method selector attributes, you can easily differentiate between such requests without using multifaceted controller actions.