Why is HttpGet required only for some actions?

Question

Let me sketch the situation first:

I have a basic controller which looks like this:

public class SearchRequestController : ApiController
{
    public IEnumerable<ObjectA> GetAllRequests() {...}
    {}
    public IEnumerable<ObjectA> GetLatestRequest() {...}
    {}
}

Using the following routing

    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
        );
    }

I can easly use the functions as follows

 Http://myServer/myvirtualdirectory/api/SearchRequest/GetAllRequests
 Http://myServer/myvirtualdirectory/api/SearchRequest/GetLatestRequest

Now i wanted to add the following controller

 public class UserController : ApiController
 {
    public IEnumerable<UserObject> SearchUsersByInput() {...}
 }

But the following GET doesn't work

 Http://myServer/myvirtualdirectory/api/User/SearchUsersByInput

 I'm getting a 405: {"Message":"The requested resource does not support http method 'GET'."} 

It works however when I change my function as follows:

 public class UserController : ApiController
 {
  [HttpGet]
  public IEnumerable<UserObject> SearchUsersByInput() {...}
 }

Question: Could someone explain the origin of this behavior? Have I done something wrong or is there something wrong with my routing?

Answer 1

Please refer to the post here

You will see that you can use naming convention (which is why the methods with Get in the name work), or you can explicitly specify the HTTP method for an action by decorating the action with the correct HTTP attribute.