Question

So, I’ve been trying for a few hours now to workaround something that should theoretically be very simple. Let’s take this sample url:

http://sample.com/products/in/texas/dallas

This maps onto a specific route:

routes.MapRoute(
    "products",
    "products/in/{state}/{city}",
    new { controller = "Products", action = "List", state = UrlParameter.Optional, city = UrlParameter.Optional });

In my action method, I can do lookups to make sure “texas” and “dallas” exist, and that “dallas” exists within Texas. That’s all fine and dandy. However, in the situation where the city doesnt exist (either because the geo is incorrect, or mispelled), I want it to back up the state level. Example:

http://sample.com/products/in/texas/dallax

That should issue a redirect to

http://sample.com/products/in/texas

The “easy” way to do this was to simply issue a Redirect call like so:

return Redirect("/products/in/" + stateName);

However, I’m trying to decouple this from the URL structure; for example, if we ever decided to change how the route looks (say, change the pattern to products/around/{state}/{city}), then I would have to know that I need to make updates to this controller to fix the URL redirect.

If I can make a solution that just inspects the route values and can figure things out, then I don’t have to worry if I change the route pattern, because the route values could still be figured out.

Ideally, I would have liked to do something like this:

return RedirectToRoute(new { controller = "Products", action = "List", state = state });

(Note, that is is a simplified example; the “required” route pieces like controller name and action method name would be determined by Generic argument and Expression inspection respectively).

That actually performs the redirect, HOWEVER, the route values from the current request get appended onto the redirect and thus you get in a redirect loop (note that I didn’t include the city route value in the route object). How do I stop the “city” route value from being included in this redirect?

I’ve tried the following things to get rid of the route value:

1. Compose my own RouteValueDictionary / anonymous route data object and pass that to the overload of RedirectToRoute.
2. Create my own action result to inspect RouteTable.Routes and find the route myself, and do the replacement of the tokens myself. This seems the most “kludgy”, and would seem to be re-inventing the wheel.
3. Make a method like RedirectWithout that takes a key value and calls RedirectToRouteResult.RouteValues.Remove(key) – which also didnt work.
4. I’ve also attempted to add a null value for the key I don’t want to add; however, this alters the route to something that isnt correct – ie new { controller = "Products", action = "List", state = stateName, city = (string)null } issues a redirect to /Products/List?state=Texas which is not the right URL.

It all seems to stem from the RedirectToRoute taking the current request context to construct the virtual path data. Is there a workaround?

Answer 1

If you were using T4MVC, you should be able to do something like this:

return RedirectToAction(MVC.Products.List(state, null));

Have you tried this?

return RedirectToRoute(new 
{
    controller = "Products", 
    action = "List", 
    state = state,
    city = null, 
});

Reply to comments

Maybe MVC is confused because your optional parameter is not at the end. The below should work with the above RedirectToRoute that specifies city = null:

routes.MapRoute(
    "products",
    "products/in/{state}/{city}",
    new
    {
        controller = "Products",
        action = "List",
        // state = UrlParameter.Optional, // only let the last parameter be optional
        city = UrlParameter.Optional 
    });

You can then add another route to handle URL’s where state is optional:

routes.MapRoute(null, // I never name my routes
    "products/in/{state}",
    new
    {
        controller = "Products",
        action = "List",
        state = UrlParameter.Optional 
    });