title: How to modify FOSUserBundle unique validator?
body: <p>I'm trying to modify the way FOSUSerBundle validates the username/email when the user registers, because I need to check if the user was previously registered, but he has unsubscribed, through status flag in the entity. I think the best way is check if email is previously on the database, excluding those who the flag <code>unsubscribed</code> is set to true, but how I do this?</p>
  
  <p>So, I see how validates with <code>UniqueValidator</code> class, but I don't understand how it works. It would be great if anyone could explain it too.</p>
  
  <p>Thanks.</p>