title: Adding item to filtered result from ember-data
body: <p>I have a <code>DS.Store</code> which uses the <code>DS.RESTAdapter</code> and a <code>ChatMessage</code> object defined as such:</p>
  
  <pre><code>App.ChatMessage = DS.Model.extend({
      contents: DS.attr('string'),
      roomId:   DS.attr('string')
  });
  </code></pre>
  
  <p>Note that a chat message exists in a room (not shown for simplicity), so in my chat messages controller (which extends <code>Ember.ArrayController</code>) I only want to load messages for the room the user is currently in:</p>
  
  <pre><code>loadMessages: function(){ 
      var room_id = App.getPath("current_room.id");
      this.set("content", App.store.find(App.ChatMessage, {room_id: room_id}); 
  }
  </code></pre>
  
  <p>This sets the <code>content</code> to a <code>DS.AdapterPopulatedModelArray</code> and my view happily displays all the returned chat messages in an <code>{{#each}}</code> block.</p>
  
  <p>Now it comes to adding a new message, I have the following in the same controller:</p>
  
  <pre><code>postMessage: function(contents) {
      var room_id = App.getPath("current_room.id");
      App.store.createRecord(App.ChatMessage, {
          contents: contents,
          room_id: room_id
      });
  
      App.store.commit();
  }
  </code></pre>
  
  <p>This initiates an ajax request to save the message on the server, all good so far, but it doesn't update the view. This pretty much makes sense as it's a filtered result and if I remove the room_id filter on <code>App.store.find</code> then it updates as expected.</p>
  
  <p>Trying <code>this.pushObject(message)</code> with the message record returned from <code>App.store.createRecord</code> raises an error.</p>
  
  <p>How do I manually add the item to the results? There doesn't seem to be a way as far as I can tell as both <code>DS.AdapterPopulatedModelArray</code> and <code>DS.FilteredModelArray</code> are immutable.</p>