How can I overload ASP.NET MVC Actions based on the accepted HTTP verbs?

Question

Wanted to use the same URL for a GET/PUT/DELETE/POST for a REST based API, but when the only thing different about the Actions is which HTTP verbs it accepts, it considers them to be duplicate!

"Type already defines a member called 'Index' with the same parameter types."

To which I said, so what? This one only accepts GET, this one only accepts POST... should be able to be co-exist right?

How?

Answer 1

That's not ASP.NET MVC limitation or whatever. It's .NET and how classes work: no matter how hard you try, you cannot have two methods with the same name on the same class which take the same parameters. You could cheat using the [ActionName] attribute:

[HttpGet]
[ActionName("Foo")]
public ActionResult GetMe()
{
   ...
}

[HttpPut]
[ActionName("Foo")]
public ActionResult PutMe()
{
   ...
}

[HttpDelete]
[ActionName("Foo")]
public ActionResult DeleteMe()
{
   ...
}

[HttpPost]
[ActionName("Foo")]
public ActionResult PostMe()
{
   ...
}

Of course in a real RESTFul application the different verbs would take different parameters as well, so you will seldom have such situations.

You may take a look at SimplyRestful for some ideas about how your routes could be organized.

Answer 2

While ASP.NET MVC will allow you to have two actions with the same name, .NET won't allow you to have two methods with the same signature - i.e. the same name and parameters.

You will need to name the methods differently use the ActionName attribute to tell ASP.NET MVC that they're actually the same action.

That said, if you're talking about a GET and a POST, this problem will likely go away, as the POST action will take more parameters than the GET and therefore be distinguishable.

So, you need either:

[HttpGet]
public ActionResult ActionName() {...}

[HttpPost, ActionName("ActionName")]
public ActionResult ActionNamePost() {...}

Or:

[HttpGet]
public ActionResult ActionName() {...}

[HttpPost]
public ActionResult ActionName(string aParameter) {...}

Answer 3

Another option is to have a single method that accepts all and distinguishes between HttpMethod and calls the appropriate code from there. E.g.

            string httpMethod = Request.HttpMethod.ToUpperInvariant();

            switch (httpMethod)
            {
                case "GET":
                    return GetResponse();

                case "POST":
                    return PostResponse();

                default:
                    throw new ApplicationException(string.Format("Unsupported HttpMethod {0}.", httpMethod));
            }

Answer 4

As a workaround you can add to one of the methods an extra argument with a default value, just to bypass the limitation and be able to build.

Of course take in mind that this is not the most recommended way of doing things, and also you will have to make clear in your code (by the parameter name or via comments) that this is an extra argument just to allow it to build, and of course make sure that you have decorated your attributes correctly.