title: Authorization on an association with CanCan,Devise and Rolify
body: <p>I have the current database estructure in my application:</p>
  
  <pre><code>Publisher has_many videos, has_many users
  Video      belongs_to publisher
  User       belongs_to publisher
  </code></pre>
  
  <p>I want to be able to give permissions to the users based on the publisher, but the object that actually gets edited it's the video object. </p>
  
  <p>Meaning that an User X can edit videos from publisher 1 and 2 but User Y can only edit videos from publisher 2 and 3 and so on. I'm pretty sure this can be done with the CanCan, Devise, Rolify combo.</p>
  
  <p>Can anyone point me in the right direction here?</p>