Mapping Validation Attributes From Domain Entity to DTO

Question

I have a standard Domain Layer entity:

public class Product
{
    public int Id { get; set; }

    public string Name { get; set; }

    public decimal Price         


        

Answer 1

If you use hand-written domain entities, why not put your domain entities in their own assembly and use that same assembly both on the client and server. You can reuse the same validations.

Answer 2

I've been considering this as well for a while now. I totally understand Brad's reply. However, let's assume I want to use another validation framework that is suitable for annotating both domain entities and view models.

The only solution I can come up with on paper that still works with attributes would be to create another attribute that "points" to a domain entity's property that you are mirroring in your view model. Here's an example:

// In UI as a view model.
public class UserRegistration {
  [ValidationDependency<Person>(x => x.FirstName)]
  public string FirstName { get; set; }

  [ValidationDependency<Person>(x => x.LastName)]
  public string LastName { get; set; }

  [ValidationDependency<Membership>(x => x.Username)]
  public string Username { get; set; }

  [ValidationDependency<Membership>(x => x.Password)]
  public string Password { get; set; }
}

A framework like xVal could possibly be extended to handle this new attribute and run the validation attributes on the dependency class' property, but with your view model's property value. I just haven't had time to flesh this out more.

Any thoughts?