Question

I have this simple User Area in my MVC 4 project.

public class UserAreaRegistration : AreaRegistration
{
    public override string AreaName { get { return "User"; } }

    public override void RegisterArea(AreaRegistrationContext context)
    {
        context.MapRoute("User_Constraint",
                "{userName}/{controller}/{action}/{id}",
                new { userName = string.Empty, controller = "Products", action = "Index", id = UrlParameter.Optional },
                new { userName = new UserNameRouteConstraint() },
                new[] { "T2b.Web.Areas.User.Controllers" }
            );
    }
}

To make sure the User Name exists I have a RouteConstraint called UserNameRouteConstraint()

All this does is a simple lookup in my users table and return true if the user has been found.

So far so good, this construction works fine!

Now; My view in the User Area has the following line of code

@Html.ActionLink("More information", "details", new {id = product.Guid})

This single line causes the UserNameRouteConstraint() to be called….

How and why!? If I write the link in plain HTML (see example below) it works well, but I want to keep to the MVC Principles as close as possible.

<a href="/username/Products/details/@product.Guid">More information</a>

Is there any way to prevent the RouteConstraint call?

Answer 1

Whenever routes are generated the constraints are processed.

You can add this check to stop the constraint depending on whether the constraint is handling an incoming request or generating a URL from a function like ActionLink:

public bool Match(HttpContextBase httpContext, Route route, string parameterName, RouteValueDictionary values, RouteDirection routeDirection)
{
    if(routeDirection == RouteDirection.UrlGeneration)
        return false;

    ...
}