title: Cancancan ability for specific case
body: <p>I use <code>cancancan</code> gem for role based authorization rules. I need to preform something like:</p>
  
  <pre><code>can :read, Post, Post.status = 1
  </code></pre>
  
  <p>This means that user can read post with status = 1. How can i do that?</p>