How do the httppost, httpput etc attributes in ASP.NET MVC 2 work?

Question

In ASP.NET MVC 2, a couple of new action filter attributes were introduced, as "shorthand" for attributes in ASP.NET MVC 1; for example, applying the HttpPostAttribute does the same thing as applying [AcceptVerbs(HttpVerbs.Post)] to an action method.

In addition, with the more verbose syntax, it is possible to combine different methods, in order to allow for example both Post and Delete.

Now I'm wondering: how do the new attributes work? If I apply both [HttpPost] and [HttpDelete], will ASP.NET MVC 2 allow both or require both (thus allowing nothing)?

Answer 1

Looking at the code for ActionMethodSelector, it appears that all action method attributes must return true for IsValidForRequest before that action will be added to the set of possible matching methods. Since it's not possible for HttpPost and HttpDelete to return IsValidForRequest for the same request, I would expect that using both will prevent that action from ever matching any request.

Here's a telling comment from the code:

private static List RunSelectionFilters(...) {
// remove all methods which are opting out of this request
// to opt out, at least one attribute defined on the method must return false

(emphasis mine)

Note that you can still use AcceptVerbs and explicitly OR the verbs if you need to match either.

EDIT -- here's an HttpPostOrDelete attribute for you.

[AttributeUsage( AttributeTargets.Method, AllowMultiple = false, Inherited = false )]
public class HttpPostOrDeleteAttribute : ActionMethodSelectorAttribute
{
    private static readonly AcceptVerbsAttribute _innerPostAttribute = new AcceptVerbsAttribute( HttpVerbs.Post );
    private static readonly AcceptVerbsAttribute _innerDeleteAttribute = new AcceptVerbsAttribute( HttpVerbs.Delete );

    public override bool IsValidForRequest( ControllerContext controllerContext, System.Reflection.MethodInfo methodInfo )
    {
        return _innerDeleteAttribute.IsValidForRequest( controllerContext, methodInfo )
               || _innerPostAttribute.IsValidForRequest( controllerContext, methodInfo );
    }
}