Why is ASP.NET-MVC Routing's UrlParameter.Optional ignored when using this Regex?

Question

This is a stripped down example of a problem I was having this morning with ASP.NET MVC's URL routing.

Fairly simple, I wanted a route's Action to be called, whether or not the parameter on the end was supplied.

This route works fine, matching both /apple/ and /apple/test/

routes.MapRoute(
    "Working Route",
    "apple/{parameter}",
    new { 
        controller = "Apple", 
        action = "Action", 
        parameter = UrlParameter.Optional
    },
    new { parameter = @"([a-z0-9\.-]+)" }
);

However, this second route will only match /banana/test/ and the like. When I try /banana/, the router just passes right over it and returns the catch-all 404 error.

routes.MapRoute(
    "Non-Working Route",
    "banana/{parameter}",
    new { 
        controller = "Banana", 
        action = "Action", 
        parameter = UrlParameter.Optional
    },
    new { parameter = @"([a-z0-9]+)" }
);

The only difference is the Regex validation of the parameter, but as it's quite a simple Regex match, they should both work perfectly fine for a URL like /banana/, yet the second route just fails to recognise it.

I side-stepped my problem by just changing the Regex on route #2 to match that on route #1, and accept the '.' and '-' characters, I just wondered if anyone knows why this seems to be happening.

EDIT:

Here are the Controllers and Actions that I'm using for my example. Nothing fancy here.

public class AppleController : Controller
{
    public ActionResult Action(string parameter)
    {
        if (parameter == null)
        {
            parameter = "No parameter specified.";
        }
        ViewData["parameter"] = parameter;
        return View();
    }
}

public class BananaController : Controller
{
    public ActionResult Action(string parameter)
    {
        if (parameter == null)
        {
            parameter = "No parameter specified.";
        }
        ViewData["parameter"] = parameter;
        return View();
    }
}

So my problem is that /apple/ would display "No parameter specified.", while /banana/ gives me an undesired 404 instead.

So far..

Using parameter = URLParameter.Optional in the Route declaration: Route #1 works perfectly, Route #2 doesn't match without the parameter.

Using parameter = "" in the Route declaration: Both Route #1 & Route #2 fail to match when the parameter is left off the URL.

Declaring parameter = "" in the Action method signature: Not possible due to .NET version.

Removing all other routes has no effect.

Something else is going on. I'm reproducing your set up as best I can tell and both routes work for me, with and without the parameter. Odd. — nkirkes
– nkirkes, Commented Feb 10, 2011 at 17:14
Just to make sure, your default route should be coming after the specified routes (most to least specific) when you register them. Can you confirm this is the case? — nkirkes
– nkirkes, Commented Feb 10, 2011 at 17:15
My default route is a catch-everything route that is declared last. The ones above are the first two routes declared in my Global.asax.cs file. — Ben Jenkinson
– Ben Jenkinson, Commented Feb 11, 2011 at 9:00

Max Toro · Accepted Answer · 2014-04-26 13:38:28Z

4

If the token is optional then whatever regex constraint you use must also reflect that, e.g. (foo)?.

I was able to reproduce this issue with ASP.NET MVC 2 on .NET 4 . Then I upgraded to ASP.NET MVC 3 and everything worked as expected. The solution I present above does not work with ASP.NET MVC 2, but it works with ASP.NET MVC 3, so I can only assume this is a bug on v2 that is now fixed in v3.

You can reference v2, and use this on web.config to test with v3:

<runtime>
   <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
         <assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" />
         <bindingRedirect oldVersion="1.0.0.0-2.0.0.0" newVersion="3.0.0.0" />
      </dependentAssembly>
   </assemblyBinding>
</runtime>

edited Apr 26, 2014 at 13:38

answered Feb 10, 2011 at 19:59

Max Toro

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2 Comments

Ben Jenkinson Over a year ago

If that is true, then why does the Regex constraint in Route #1 above work as intended without reflecting that?

Ben Jenkinson Over a year ago

Sorry I forgot to actually mark this as the answer. It does seem that this is a quirk of ASP.NET MVC 2.

nkirkes · Accepted Answer · 2011-02-10 17:01:02Z

0

2nd EDIT

Matching ~/fruit/ and ~fruit/apple

routes.MapRoute(
    "Working Route",
    "Fruit/{fruit}",
    new
    {
        controller = "Fruit",
        action = "Index",
        fruit = ""
    },
    new { fruit = @"([a-z0-9\.-]+)" }
);

public ActionResult Index(string fruit)
{
    ViewData["fruit"] = !String.IsNullOrEmpty(fruit) ? fruit : "None specified.";
    return View();
}

Matching ~/banana/ and ~/banana/yellow

routes.MapRoute(
    "Non-Working Route",
    "Banana/{color}",
    new
    {
        controller = "Banana",
        action = "Index",
        color = ""
    },
    new { color = @"([a-z0-9]+)" }
);

public ActionResult Index(string color)
    {
        ViewData["Color"] = color;
        return View();
    }

1st EDIT

Try actually setting the parameter as optional on the action signature, such that: string parameter = ""

I'm not getting that behavior. Both routes work for me as you're describing them (the second route throws a 404 if I add a "-" to the route, but that's expected). What does your action method signature look like?

I set my route (and controller/view) to look like:

routes.MapRoute(
    "Working Route",
    "Fruit/{fruit}",
    new
    {
        controller = "Fruit",
        action = "Index",
        fruit = UrlParameter.Optional
    },
    new { fruit = @"([a-z0-9]+)" }
);

And my Index() action looks like:

public ActionResult Index(string fruit = "")
{
    ViewData["fruit"] = fruit;
    return View();
}

edited Feb 10, 2011 at 17:01

answered Feb 10, 2011 at 15:53

nkirkes

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10 Comments

Ben Jenkinson Over a year ago

I've added my example controllers above, and tried to explain my aim a little. I want to be able to catch the null state in the controller, where the parameter I've declared as optional isn't included in the URL. When I use the second ("Non-Working") route and drop the parameter entirely, it just falls through to the 404 instead of matching (but as far as I can tell, it should match).

nkirkes Over a year ago

It's because your action method is explicitly looking for a string to passed in. You can either make it optional in the signature as I mention in my Edit, and manage the empty string case internally, or you can change the route to be an empty string ("") instead of the UrlParameter.Optional.

nkirkes Over a year ago

FWIW, it's still not clear to me why your initial route would work, but the second route would not. I wasn't able to reproduce that specific issue.

Ben Jenkinson Over a year ago

That's basically my question, why does it work for one, yet not the other? I'm unable to set a default in the Action method signature, I get a build error "Default parameter specifiers are not permitted". If I set parameter = "" on the Route instead of UrlParameter.Optional, then neither of the routes work. They both fall through to 404 when it's not specified.

nkirkes Over a year ago

Ah. What version of .NET are you working in? Optional parameters like that are specific to .NET 4.0. Sorry, jumped the gun. So your only real option then, in your current configuration, is to change the routing to read: fruit = "" instead of using the UrlParameter.Optional. Just tested that theory and it worked as expected.

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