title: IValidatableObject not triggered
body: <p>I'm trying to make use of the IValidatableObject as described here <a href="http://davidhayden.com/blog/dave/archive/2010/12/31/ASPNETMVC3ValidationIValidatableObject.aspx" rel="nofollow">http://davidhayden.com/blog/dave/archive/2010/12/31/ASPNETMVC3ValidationIValidatableObject.aspx</a>.</p>
  
  <p>But it just wont fire when I'm trying to validate, the <code>ModelState.IsValid</code> is always <code>true</code>.</p>
  
  <p>Here is my model code:</p>
  
  <pre><code>[MetadataType(typeof(RegistrationMetaData))]
  public partial class Registration : DefaultModel
  {
      [Editable(false)]
      [Display(Name = "Property one")]
      public int PropertyOne { get; set; }
  }
  
  public class RegistrationMetaData :IValidatableObject
  {
      [Required(ErrorMessage = "Customer no. is required.")]
      [Display(Name = "Customer no.")]
      public string CustomerNo { get; set; }
  
      [Display(Name = "Comments")]
      public string Comments { get; set; }
  
      public IEnumerable&lt;ValidationResult&gt; Validate(ValidationContext validationContext)
      {
          if (new AccountModel().GetProfile(CustomerNo) == null)
              yield return new ValidationResult("Customer no. is not valid.", new[] { "CustomerNo" });
      }
  }
  </code></pre>
  
  <p>I extend a LINQ to SQL table called <code>Registration</code>, my first guess was that this is not possible to do on a Meta class, but I'm not sure?</p>
  
  <p>I do not get any errors, and it builds just fine, but the <code>Validate</code> method will not fire. What have I missed?</p>