Question

Given this route:

routes.MapRoute("home", "{action}/{id}",
  new { controller = "home", action = "index", id = UrlParameter.Optional });

…and this action:

public ActionResult Hi(string id) {
   return Content("hello, id: " + id);
}

Question #1
What is the response for:

GET http://localhost:2247/hi/7?id=55 HTTP/1.1

Question #2
What is the response for:

POST http://localhost:2247/hi/7?id=55 HTTP/1.1
Content-Length: 4
Content-Type: application/x-www-form-urlencoded

id=3

---

I believe this is a bug and the route value should always have precedence, since the URL is what identifies a resource. If you write a POST, PUT or DELETE action you expect the id coming from the URL, not from the body of the request. This could cause changes to a different resource, and can be exploited by malicious users.

---

After doing some research found that the issue is the default ValueProviderFactory registration order, where FormValueProviderFactory comes before RouteDataValueProviderFactory. Instead of messing with the order I created a CustomModelBinderAttribute:

[AttributeUsage(AttributeTargets.Parameter)]
public sealed class FromRouteAttribute : CustomModelBinderAttribute, IModelBinder {

   public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) {

      bindingContext.ValueProvider = new RouteDataValueProvider(controllerContext);

      return ModelBinders.Binders.DefaultBinder.BindModel(controllerContext, bindingContext);
   }

   public override IModelBinder GetBinder() {
      return this;
   }
}

…which you can use like this:

public ActionResult Hi([FromRoute]string id) {
   return Content("hello, id: " + id);
}

Answer 1

In ASP.NET MVC 3 RC2:

• GET: Response: hello, id: 7
• POST: Response: hello, id: 3

And here’s the test view:

<a href="/hi/7?id=55">GET</a>
<form action="/hi/7?id=55" method="POST">
    <input type="hidden" name="id" value="3" />
    <input type="submit" value="POST" />
</form>

So here is the evaluation precedence order:

1. POST body parameter
2. Route
3. Query string parameter

And by the way the exact same result is obtained with ASP.NET MVC 2.0.