Question

I’d like to maintain ASP.NET MVC 4’s existing controller/action/id routing with default controller = Home and default action = Index, but also enable controller/id to route to the controller’s index method as long as the second item is not a known action.

For example, given a controller Home with actions Index and Send:

/Home/Send -> controller's Send method
/Home -> controller's Index method
/Home/Send/xyz -> controller's Send method with id = xyz
/Home/abc -> controller's Index method with id = abc

However, if I define either route first, it hides the other one. How would I do this?

Answer 1

In case, that the list of your actions (e.g. Send) is well known, and their (action) names cannot be the same as some ID value, we can use our custom ConstraintImplementation:

public class MyRouteConstraint : IRouteConstraint
{
  public readonly IList<string> KnownActions = new List<string> 
       { "Send", "Find", ... }; // explicit action names

  public bool Match(System.Web.HttpContextBase httpContext, Route route
                  , string parameterName, RouteValueDictionary values
                  , RouteDirection routeDirection)
  {
    // for now skip the Url generation
    if (routeDirection.Equals(RouteDirection.UrlGeneration))
    {
      return false; // leave it on default
    }

    // try to find out our parameters
    string action = values["action"].ToString();
    string id = values["id"].ToString();

    // id and action were provided?
    var bothProvided = !(string.IsNullOrEmpty(action) || string.IsNullOrEmpty(id));
    if (bothProvided)
    {
      return false; // leave it on default
    }

    var isKnownAction = KnownActions.Contains(action
                           , StringComparer.InvariantCultureIgnoreCase);

    // action is known
    if (isKnownAction)
    {
      return false; // leave it on default
    }

    // action is not known, id was found
    values["action"] = "Index"; // change action
    values["id"] = action; // use the id

    return true;
  }

And the route map (before the default one – both must be provided), should look like this:

routes.MapRoute(
  name: "DefaultMap",
  url: "{controller}/{action}/{id}",
  defaults: new { controller = string.Empty, action = "Index", id = string.Empty },
  constraints: new { lang = new MyRouteConstraint() }
);

Summary: In this case, we are evaluating the value of the “action” parameter.

• if both 1) action and 2) id are provided, we won’t handle it here.
• nor if this is known action (in the list, or reflected…).
• only if the action name is unknown, let’s change the route values: set action to “Index” and action value to ID.

NOTE: action names and id values need to be unique… then this will work