title: Tell ember.js to use different key for its model's "id"
body: <p>I am stuck in a situation where I shouldn't return <code>id</code> field in the API endpoint. I need to tell ember to use <code>slug</code> field for / instead of <code>id</code>.</p>
  
  <p>I tried <code>DS.RESTAdapter.map('App.Post', id: {key: 'slug'})</code>. While this works perfectly fine for <code>App.Post.find("a-slug-name")</code>, It messes up for <code>App.Post.find()</code> resulting in adding a new model every time it is called. And also assigning <code>id</code> to null. </p>
  
  <p>So how should I do this.</p>