ASP.NET MVC: Creating a URL From Route Values

I’m currently building some JSON services for a client using ASP.NET MVC. One of the things I want to implement is HATEOS (read the link) so I need to be able to build the URLs (or URIs) of the endpoints that I can then embed into the JSON I return to the client.

I wanted to be able to take some route values, controller=”abc”, action=”xyz”, id=10, and return a virtual path. Unfortunately System.Web.Routing makes this a bit of trial, but you can make it work. I’ve wrapped my implementation up in a little UriBuilder class. Here’s a test showing it working:

[Test]
public void CreateUriFromRouteValues_should_create_the_correct_virtual_path()
{
    var routes = new RouteCollection();
    routes.MapRoute(
        "ProgRock",
        "{band}/{album}/{track}",
        new { controller = "Home", action = "Index", id = UrlParameter.Optional });

    var uriBuilder = new UriBuilder(() => routes, () => new FakeHttpContext());

    var uri = uriBuilder.CreateUriFromRouteValues(new
    {
        band = "Yes",
        album = "Fragile",
        track = "Roundabout",
        info = "great keyboard solo"
    });

    uri.ShouldEqual("/Yes/Fragile/Roundabout?info=great%20keyboard%20solo");
}

And here’s the implementation:

public interface IUriBuilder
{
    string CreateUriFromRouteValues(object values);
}

public class UriBuilder : IUriBuilder
{
    private readonly Func<RouteCollection> getRouteCollection;
    private readonly Func<HttpContextBase> getHttpContext;

    public UriBuilder(Func<RouteCollection> getRouteCollection, Func<HttpContextBase> getHttpContext)
    {
        this.getRouteCollection = getRouteCollection;
        this.getHttpContext = getHttpContext;
    }

    public string CreateUriFromRouteValues(object values)
    {
        var routeValues = new RouteValueDictionary(values);

        var routeData = new RouteData();
        var requestContext = new RequestContext(getHttpContext(), routeData);
        var virtualPathData = getRouteCollection().GetVirtualPath(requestContext, routeValues);
        if (virtualPathData == null)
        {
            throw new ApplicationException("virtualPathData is null");
        }
        return virtualPathData.VirtualPath;
    }
}

In order to unit test it, you have to fake the HttpContext. Here’s my fake implementation:

 

public class FakeHttpContext : HttpContextBase
{
    public override HttpRequestBase Request
    {
        get { return new FakeRequest(); }
    }

    public override HttpResponseBase Response
    {
        get { return new FakeResponse(); }
    }
}

public class FakeRequest : HttpRequestBase
{
    public override string ApplicationPath
    {
        get { return "/"; }
    }
}

public class FakeResponse : HttpResponseBase
{
    public override string ApplyAppPathModifier(string virtualPath)
    {
        return virtualPath;
    }
}

You can also use the fake HttpContext if you want to be able to create URLs outside an ASP.NET application where HttpContext.Current is null.

In the application, I register my route and httpContext provider delegates like this:

public class MvcInstaller : IWindsorInstaller
{
    public void Install(IWindsorContainer container, IConfigurationStore store)
    {
        container.Register(
                Component.For<Func<HttpContextBase>>()
                    .Instance(() => new HttpContextWrapper(HttpContext.Current)),
                Component.For<Func<RouteCollection>>()
                    .Instance(() => RouteTable.Routes)
            );
    }
}