title: Entity framework + validation annotation
body: <p>I want to use a validation anotation.
  I have already a model implemented by entity framework.
  I need data validation and I know that there is a data anotation which is very nice...
  But I really don't know how can I use it with entity framework correct.</p>
  
  <p>Should I edit entities? Or should I write separated class? Or should I write class which are inherit from entities?</p>
  
  <p>Can you tell me the best way I should use?</p>
  
  <p>I want to write as few code as it is possible.</p>