MEF and exporting based on Metadata

OK I'm pretty sure this is something blindingly obvious but I'm not finding it.

I'm trying to export a object from MEF container based on it's Metadata.

I've seen this done in tutorials like this one:

http://blog.maartenballiauw.be/post/2009/04/21/ASPNET-MVC-and-the-Managed-Extensibility-Framework-%28MEF%29.aspx

However my export doesn't have the Metadata property that is necessary for this to work. What could be the problem there?

[Export(typeof(IController))]
[ExportMetadata("controllerName","Home")]
[PartCreationPolicy(CreationPolicy.NonShared)]
public class HomeController : Controller{}

and again

public class MyControllerFactory : IControllerFactory
{
    private readonly CompositionContainer _container;

    public MyControllerFactory(CompositionContainer container)
    {
        _container = container;
    }

    public IController CreateController(System.Web.Routing.RequestContext requestContext, string controllerName)
    {
        var controllerExport = _container.GetExports<IController>().
                Where(exp => exp.Metadata) //Here it doesn't have the Metadata property.
    }
}

I understand that the GetExports returns a collection of Lazy that do of course not have the Metadata property but it's assumed in most tutorials I look through.

How do I do this correctly?

EDIT

This is what I did:

 public interface IControllerMetaData
{
    string Name { get; }
    string Subdomain { get; }
}

[MetadataAttribute]
[AttributeUsage(AttributeTargets.Class, AllowMultiple=false)]
public class ControllerMetadataAttribute : ExportAttribute
{
    public ControllerMetadataAttribute(string name, string subdomain)
        : base(typeof(IControllerMetaData))