What do the curly braces mean in a route in MVC? - asp.net-mvc

Question

I'm setting up my routes with an MVC project but im a little confused about the curly braces...
If I have...
routes.MapRoute( "Music", "Music/{name}", new { } );
What is the purpose of the curly braces around name, does this get passed to something? Or does this map to something if I pass a default object in?

Answer 1

They are parameter names that are used in routing requests. For example the default route defines three of them:
{controller}/{action}/{id}
controller and action parameters are for finding your controller action. id parameter can be used as an input in those actions.
When you define a custom route you have to provide controller and action parameters. If they are not defined in your URL, you should provide default values so MVC knows what action to run when a request matches that route.
routes.MapRoute("Music",
"Music/{name}",
new { controller="Music", action="SomeAction" });
Other parameters like id or name like you defined can be used to provide input to actions. In your example, name parameter is passed to matching action like this:
public ActionResult SomeAction(string name)
{
//do something
}

Answer 2

The curlybraces indicate a kind of named wildcard.
The "Music/Index" route will only match the URL Music/Index and nothing else
The "Music/{Name}" route will match any URLs starting with Music, and having anything after the slash. It will match both the URLs Music/metallica and Music/madonna.
With the curly brace, you'll be able to pick up "metallica" or "madonna" from the above URLS as routevalues.
As a final example: With ASP.NET MVC, there's always a standard route. {controller}/{action}/{id}. This route will catch URLs like Music/genre/rock or Product/edit/5.
The resulting routevalues for these two will be:
controller=music, action=genre and id=rock for the first one
controller=product, action=edit and id=5 for the last one.

Answer 3

I'll try to provide a less contrived example.
Routes in ASP.NET MVC are placed into a dictionary, and when there's an incoming request, the MVC pipeline looks at the request and tries to determine what Controller and Action to route it to.
So let's say I have the following controllers: Home, Forum, and Article
And while we're at it, let's say I have the following actions: View, Edit, Create on both the Forum and Article controllers.
Those braces allow me to create one route for both:
routes.MapRoute("Viewing",
{controller}/{action}/{id},
new {controller = "Article", action="" }, //The article controller has precedence
new { controller = "Article|Forum" } //contrived for this example
);
Those braces mean that whatever controller they put in (as long as it's Article or Forum based on the Constraints), the same route works. This keeps me from having to have a route for each and every action in the Forum and Article controller.
I could have just as easily made two routes:
routes.MapRoute("Articles",
article/{action}/{id},
new {controller = "Article" } //The article controller has precedence
);
routes.MapRoute("Forums",
forum/{action}/{id},
new { controller = "forum" }
);
But there's duplication there that doesn't need to be there.
Routes are also pretty tricky things, in that order matters. The top route will be evaluated before the bottom route. If it matches the top route's structure, it will go to that action, even if that's not the right action.
Phil Haack has a Route Debugger that helps with this. And I've also taken his source code and modified it so that you can make it a control and put it on all your pages as a partial (and hopefully you will also put code on there that would only allow internal folks to see it).