title: Sonata Admin Enable action
body: <p>I'm using Symfony for make a web site and I installed sonata admin Bundle.
  I have an entity with a boolean variable (enable).
  I would like when this variable change state to True the other one for the same table go to False. In fact I would like only one variable (enable) for the same table is at True. </p>
  
  <p>So I thought to change setEnable directly in my Entity but I can't get the repository from my Entity class.</p>
  
  <p><em>How can I get my repository from my Entity Class ?</em></p>