title: Ember custom model save
body: <p>In my application I have a model <code>post</code>, it has properties <code>user_likes</code> and <code>user_shares</code>, a user can share and like a post of course...</p>
  
  <p>a save action results in a PUT for /posts/:id with post as payload, but in my webserver shares and likes have different store strategies, and <strong>I need know what exactly has changed</strong> to save properly, how can I do it with ember?</p>