title: EntityType 'Uri' has no key defined
body: <p>I have a problem with EF 4.1</p>
  
  <p>Here are my entities and context:</p>
  
  <pre><code> public class PasmISOContext : DbContext
   {
       public DbSet&lt;Avatar&gt; Avatars { get; set; }
       public DbSet&lt;User&gt; Users { get; set; }
   }
  
  namespace PasmISO.Domain
  {
      public class User
      {
          [Key]
          public string Login { get; set; }
          public string Email { get; set; }
          public string Password { get; set; }
          public Avatar Avatar { get; set; }
      }
  }
  
  namespace PasmISO.Domain
  {
      public class Avatar
      {
          [Key]
          public int Id { get; set; }
          [Required]
          public Uri Link { get; set; }
      }
  }
  </code></pre>
  
  <p>at mvc controller I have </p>
  
  <pre><code> PasmISOContext db=new PasmISOContext();
   if (db.Avatars.Count()==0)
   {
       db.Avatars.Add(new Avatar() { Link = new Uri("http://www.google.com/somelinktojpg") });
   }
  </code></pre>
  
  <p>When I run my code, I get exception:</p>
  
  <pre><code>One or more validation errors were detected during model generation:
  
      System.Data.Edm.EdmEntityType: : EntityType 'Uri' has no key defined. Define the key for this EntityType.
      System.Data.Edm.EdmEntitySet: EntityType: EntitySet �Uris� is based on type �Uri� that has no keys defined.
  </code></pre>
  
  <p>Any ideas on how to get around this?</p>