If Route doesn't exist -> go to other route using its default action?

Question

So I'm having a little problem here with routing.

There are two parts to this web application:
  1. Brochure / Display Website
  2. Internal Site / Client Application

We wanted a way to release changes for the brochure without having to do a whole release of said Web application. Visiting existing named views will take the user to a brochure page, however if it doesn't exist, it will act like they are a client and will redirect them to their company's login screen.

Global.asax:

//if view doesnt exist then url is a client and should be redirected
routes.MapRoute(
    name: "Brochure",
    url: "{id}",
    defaults: new { controller = "brochure", action = "Brochure", id = "Index" },
    namespaces: new[] { "Web.Areas.Brochure.Controllers" }
);

//This is home page
routes.MapRoute(
    name: "HomeDefault",
    url: "{client}/{action}",
    defaults: new { controller = "home", action = "index" },
    namespaces: new string[] { "Web.Controllers" }
);

Controller:

/// <summary> Check if the view exists in our brochure list </summary>
private bool ViewExists(string name) {
    ViewEngineResult result = ViewEngines.Engines.FindView(ControllerContext, name, null);
    return (result.View != null);
}

/// <summary> Generic action result routing for all pages. 
/// If the view doesn't exist in the brochure area, then redirect to interal web
/// This way, even when we add new pages to the brochure, there is no need to re-compile & release the whole Web project. </summary>
public ActionResult Brochure(string id) {
    if (ViewExists(id)) {
        return View(id);
    }

    return RedirectToRoute("HomeDefault", new { client = id });
}

This code works fine up until we log in and go to the landing page. It seems to keep the Brochure action in the route and doesn't want to go to the subsequent controller which results in a 500 error. e.g. 'domain/client/Brochure' when it needs to be: 'domain/client/Index'

Things tried but not worked:

• Changing RedirectToRoute() to a RedirectToAction() - this results in a finite loop of going back to the ActionResult Brochure(). So changing controllers through that didn't work.
• Create an ActionResult called Brochure() inside the 'HomeController'. It doesn't even get hit.
• Passed in namespaces for RedirectToRoute() as an attribute. I knew this would probably not work, but it was worth a try.

---

So the question is:
How can I get the route to act properly?

Answer 1

If you can restrict id to some subset of all values you can add that constraints to route (i.e. numbers only) to let default handle the rest.

routes.MapRoute(
    name: "Brochure",
    url: "{id}",
    defaults: new { controller = "brochure", action = "Brochure", id = "Index" },
    namespaces: new[] { "Web.Areas.Brochure.Controllers" }
    constraints : new { category = @"\d+"}
);

If you can't statically determine restrictions - automatically redirecting in your BrochureController similar to your current code would work. The only problem with sample in the question is it hits the same route again and goes into infinite redirect loop - redirect to Url that does not match first rule:

// may need to remove defaults from second route 
return RedirectToRoute("HomeDefault", new { client = id, action = "index" });

If standard constraints do not work and you must keep single segment in url - use custom constraints - implement IRouteConstraint and use it in first route. See Creating custom constraints.

Answer 2

Two ways I could have solved this issue:

Way 1

I reviewed the redirect and just passed in an action in order to get a route that has 2 segments in the url. i.e. client/Index. The Index action now handles logins - going past a custom controller.
public class HomeController : CustomController

public ActionResult Brochure(string id, string action) {
    if (ViewExists(id)) {
        return View(id);
    }

    return RedirectToAction("Index", "Home", new { client = id, action = "Index" });
}

Way 2

(from @Alexei_Levenkov)
Create a custom Route constraint so the route will be ignored if the view cannot be found.

namespace Web.Contraints {
    public class BrochureConstraint : IRouteConstraint {
        public bool Match(HttpContextBase httpContext, Route route, string parameterName, RouteValueDictionary values, RouteDirection routeDirection) {
            //Create our 'fake' controllerContext as we cannot access ControllerContext here
            HttpContextWrapper context = new HttpContextWrapper(HttpContext.Current);
            RouteData routeData = new RouteData();
            routeData.Values.Add("controller", "brochure");
            ControllerContext controllerContext = new ControllerContext(new RequestContext(context, routeData), new BrochureController());

            //Check if our view exists in the folder -> if so the route is valid - return true
            ViewEngineResult result = ViewEngines.Engines.FindView(controllerContext, "~/Areas/Brochure/Views/Brochure/" + values["id"] + ".cshtml", null);
            return result.View != null;
        }
    }
}

namespace Web {
    public class MvcApplication : System.Web.HttpApplication {
        //If view doesnt exist then url is a client so use the 'HomeDefault' route below
        routes.MapRoute(
            name: "Brochure",
            url: "{id}",
            defaults: new { controller = "brochure", action = "Brochure", id = "Index" },
            namespaces: new[] { "Web.Areas.Brochure.Controllers" },
            constraints: new { isBrochure = new BrochureConstraint() }
        );

        //This is home page for client
        routes.MapRoute(
            name: "HomeDefault",
            url: "{client}/{action}",
            defaults: new { controller = "home", action = "index" },
            namespaces: new string[] { "Web.Controllers" }
        );
    }
}

I hope this helps someone else out there.

Answer 3

There are several issues with your configuration. I can explain what is wrong with it, but I am not sure I can set you on the right track because you didn't provide the all of the URLs (at least not all of them from what I can tell).

Issues

1. Your Brouchure route, which has 1 optional URL segment named {id}, will match any URL that is 0 or 1 segments (such as / and /client). The fact that it matches your home page (and you have another route that is named HomeDefault that will never be given the chance to match the home page) leads me to believe this wasn't intended. You can make the {id} value required by removing the default value id = "Index".
2. The Brouchure route has a namespace that indicates it is probably in an Area. To properly register the area, you have to make the last line of that route ).DataTokens["area"] = "Brochure"; or alternatively put it into the /Areas/Brouchure/AreaRegistration.cs file, which will do that for you.
3. The only way to get to the HomeDefault route is to supply a 2 segment URL (such as /client/Index, which will take you to the Index method on the HomeController). The example URLs you have provided have 3 segments. Neither of the routes you have provided will match a URL with 3 segments, so if these URLs are not getting 404 errors they are obviously matching a route that you haven't provided in your question. In other words, you are looking for the problem in the wrong place.

If you provide your entire route configuration including all Area routes and AttributeRouting routes (including the line that registers them), as well as a complete description of what URL should go to what action method, I am sure you will get more helpful answers.

So the question is: How can I get the route to act properly?

Unknown. Until you describe what properly is.

Related: Why map special routes first before common routes in asp.net mvc?