title: transition after saving model of ember data
body: <p>I want to make transition after a create a post.</p>
  
  <blockquote>
    <p>post/new > click submit > rails backend successfully create post and response a json > redirect to newly created post's path</p>
  </blockquote>
  
  <p>in ember_data_example github source code. they use this approach</p>
  
  <pre><code> transitionAfterSave: function() {
       // when creating new records, it's necessary to wait for the record to be assigned
       // an id before we can transition to its route (which depends on its id)
       if (this.get('content.id')) {
         this.transitionToRoute('contact', this.get('content'));
       }
   }.observes('content.id'),
  </code></pre>
  
  <p>It works fine, because The model has ID of null when model created, and its ID would change when model saving is successful because this function observes change of models ID.</p>
  
  <p>But maybe, this function will be executed whenever model's ID property is changed.
  I'm finding some more semantic way. </p>
  
  <p>I want transition to be executed 
  when the model's status is changed to 'isDirty' = false &amp;&amp; 'isNew' == true form 'isDirty' = true, 'isNew' = false.</p>
  
  <p>How can I implement this?</p>