html.ActionLink using wrong route - asp.net

Question

I have set up the following routes so that I can use duplicate controller names (in different namespaces). This works fine but when I use html.actionlink from any controller it always includes the “CRUD” subfolder to the link.
var route1 = routes.MapRoute(
"CRUD",
"CRUD/{controller}/{action}/{id}",
new { action = "Index", id = UrlParameter.Optional }
);
route1.DataTokens["Namespaces"] = new string[] { "College.Controllers.CRUD" };
route1.DataTokens["UseNamespaceFallback"] = false;
var route2 = routes.MapRoute(
name: "Default",
url: "{controller}/{action}/{id}",
defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional },
namespaces: new[] { "College.Controllers" }
);
route2.DataTokens["Namespaces"] = new string[] { "College.Controllers" };
route2.DataTokens["UseNamespaceFallback"] = false;
So an html.actionlink in http://localhost/students/index looks like this
http://localhost/CRUD/students/Edit/1
What I want is this
http://localhost/students/Edit/1
I know I could fix this by specifying the route in the actionlink but I don’t want to do this because I want to re-scaffold in future and my changes would be overwritten.

Answer 1

The issue here is that your 2 routes are ambiguous when building the URL. There are basically 3 ways to fix this:
Add another route value to match that is not part of the URL.
Use RouteLink to specify the route by name (along with the other route value criteria to make it match).
Create a custom route to handle "constraining" it to a specific namespace or make a custom route constraint.
Since you explicitly stated the second option is unacceptable, here is an example of the first:
var route1 = routes.MapRoute(
"CRUD",
"CRUD/{controller}/{action}/{id}",
new { crud = "crud", action = "Index", id = UrlParameter.Optional }
);
route1.DataTokens["Namespaces"] = new string[] { "College.Controllers.CRUD" };
route1.DataTokens["UseNamespaceFallback"] = false;
var route2 = routes.MapRoute(
"Default",
"{controller}/{action}/{id}",
new { controller = "Home", action = "Index", id = UrlParameter.Optional }
);
route1.DataTokens["Namespaces"] = new string[] { "College.Controllers" };
route1.DataTokens["UseNamespaceFallback"] = false;
Now when you call #Html.ActionLink("Students", "Index", "Students", new { crud = (string)null }, null) it will not match the CRUD route, it will match the Default route.
To make it match the CRUD route, you have to explicitly add the route value to the ActionLink: #Html.ActionLink("Students", "Index", "Students", new { crud = "crud" }, null) or leave it out entirely: #Html.ActionLink("Students", "Index", "Students")
Constraining the Route
Here is an example of the 3rd option.
Unfortunately, we can't use a regular route constraint because Microsoft decided not to make the RequestContext object available in the IRouteConstraint interface. This means the namespace information about what controller the request is bound for is not available. So, we need to drop to a lower level and make a custom RouteBase class that implements the decorator pattern to wrap our existing Route class configuration.
This class simply checks to see if the namespace from the request matches a specific namespace before generating the URL.
public class NamespaceConstrainedRoute : RouteBase
{
private readonly string namespaceToMatch;
private readonly RouteBase innerRoute;
public NamespaceConstrainedRoute(string namespaceToMatch, RouteBase innerRoute)
{
if (string.IsNullOrEmpty(namespaceToMatch))
throw new ArgumentNullException("namespaceToMatch");
if (innerRoute == null)
throw new ArgumentNullException("innerRoute");
this.namespaceToMatch = namespaceToMatch;
this.innerRoute = innerRoute;
}
public override RouteData GetRouteData(HttpContextBase httpContext)
{
return innerRoute.GetRouteData(httpContext);
}
public override VirtualPathData GetVirtualPath(RequestContext requestContext, RouteValueDictionary values)
{
object namespaces;
if (requestContext.RouteData.DataTokens.TryGetValue("Namespaces", out namespaces)
&& namespaces is IList<string>
&& ((IList<string>)namespaces).Contains(namespaceToMatch))
{
return innerRoute.GetVirtualPath(requestContext, values);
}
// null indicates to try to match the next route in the route table
return null;
}
}
Usage
var route1 = new Route(
url: "CRUD/{controller}/{action}/{id}",
defaults: new RouteValueDictionary(new { action = "Index", id = UrlParameter.Optional }),
routeHandler: new MvcRouteHandler()
)
{
DataTokens = new RouteValueDictionary
{
{ "Namespaces", new string[] { "College.Controllers.CRUD" }},
{ "UseNamespaceFallback", false }
}
};
var route2 = new Route(
url: "{controller}/{action}/{id}",
defaults: new RouteValueDictionary(new { controller = "Home", action = "Index", id = UrlParameter.Optional }),
routeHandler: new MvcRouteHandler()
)
{
DataTokens = new RouteValueDictionary
{
{ "Namespaces", new string[] { "College.Controllers" }},
{ "UseNamespaceFallback", false }
}
};
routes.Add(
name: "CRUD",
item: new NamespaceConstrainedRoute(
namespaceToMatch: "College.Controllers.CRUD",
innerRoute: route1));
routes.Add(
name: "Default",
item: new NamespaceConstrainedRoute(
namespaceToMatch: "College.Controllers",
innerRoute: route2));
From this point, you could build your own MapRoute extension methods if you so choose to make the above configuration look cleaner.