Why are these two Actions considered ambiguous despite the parameters being different? - asp.net-mvc

Question

The current request for action 'Index' on controller type 'UsersController' is ambiguous between the following action methods:
System.Web.Mvc.ActionResult PostUser(Models.SimpleUser) on type Controllers.UsersController
System.Web.Mvc.ActionResult PostUser(Int32, Models.SimpleUser) on type Controllers.UsersController
Is happening when I try to POST website.com/users/ with form values.
When there is NO ID (website.com/users/) I want it to create a new user, when there IS an ID (/users/51 for example) I want it to update that user, so how can I make it tell the difference between these two Actions?
Here are the two actions:
[HttpPost]
[ActionName("Index")]
public ActionResult PostUser(SimpleUser u)
{
return Content("User to be created...");
}
[HttpPost]
[ActionName("Index")]
public ActionResult PostUser(int id, SimpleUser u)
{
return Content("User to be updated...");
}
Here is the MapRoute:
routes.MapRoute(
"Users",
"users/{id}",
new { controller = "Users", action = "Index" }
);

Answer 1

The main problem is there is some ambiguity between your two action methods, as model binding doesn't help decern the routing configuration. Your current routing simply points to index method.
You can still have the same URL, but it would be helpful to name your actions differently and then apply some new routes.
[HttpPost]
public ActionResult Create(SimpleUser u)
{
return Content("User to be created...");
}
[HttpPost]
public ActionResult Edit(int id, SimpleUser u)
{
return Content("User to be updated...");
}
And then in your routing try
routes.MapRoute(
"UserEdit",
"users/{id}",
new { controller = "Users", action = "Edit",
httpMethod = new HttpMethodConstraint("POST") });
routes.MapRoute(
"UserCreate",
"users",
new { controller = "Users", action = "Create",
httpMethod = new HttpMethodConstraint("POST") });
The routes will be constrained to POST events only, which means you can still add some routing for your GET methods on the same route. Such as for a list or something.

Answer 2

You must disambiguate your methods by having two different action names.
What you can do to have a RESTful API is to create your own RouteHandler class which will change the routing, dependent on whether or not the {id} value is present. The RouteHandler class is simple:
using System.Web.Mvc;
using System.Web.Routing;
public class MyRouteHandler : IRouteHandler
{
public IHttpHandler GetHttpHandler(RequestContext requestContext)
{
var routeData = requestContext.RouteData;
if (routeData.Values("id").ToString() == "0" /* our default invalid value */ )
{
var action = routeData.Values("action");
routeData.Values("action") = action + "Add";
}
var handler = new MvcHandler(requestContext);
return handler;
}
}
Next, modify RegisterRoutes() in Global.asax.cs as follows:
public static void RegisterRoutes(RouteCollection routes)
{
routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
AreaRegistration.RegisterAllAreas();
routes.Add("Default", new Route("{controller}/{action}/{id}",
new RouteValueDictionary(
new { controller = "Home",
action = "Index",
id = "0" /* our default invalid value */ }),
new MyRouteHandler()));
}
Finally, change the ActionName attribute for your Add method to "IndexAdd". When the request comes in without an id, the default invalid value will be supplied, which will alert your RouteHandler to change the method to your "Add" method.
counsellorben

Answer 3

It would be better if you consider using Create and Edit actions to achieve what you want. Generally index can be used to list all the users(in your case).
About the problem you are facing, it is arising because there is no route which does not take any id as parameter.