WCF DataService with EF CTP 5 CodeOnly DbContext

I am trying to build a WCF DataService on top of a Code Only DbContext. However as soon as I add the first DbSet property to my DbContext I get "Request Error" when accessing the .svc.

All I need to get 开发者_StackOverflow中文版the error is to have this DbContext:

public class JukeboxContext : DbContext
{
    public DbSet<Song> Songs { get; set; }
}

and then do a basic WCF DataService based on it, and the error happens when i run the service.

Any ideas on what I need to do?

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Turnes out the exception means that it can't resolve which field is the primary key. The easy way to go is to name it ID or ID - otherwise the DataServiceKey attribute will let you use composite keys