title: How to assign a record to associated model in ExtJs?
body: <p>I have a model Comment, which "hasOne" model UserDigest.
  For some reason, I want to load the UserDigest else where and then put it into the correspond Comment. Do something like this: </p>
  
  <pre><code>comment.userDigest().setData(userDigest.getData());
  </code></pre>
  
  <p>But I cannot find a method like that. Can someone tell me how to set an existing record as the data of associated model ?</p>
  
  <p>Or how to assign an existing model to associated model? Something like this:</p>
  
  <pre><code>comment.userDigest = userDigest; 
  </code></pre>