title: Ember observes async belongsTo relationship attribute on load
body: <p>I am trying observe an async belongsTo relationship attribute. I only want to observe changes that come from the api. So I am thinking of a one-way binding and observing that. I'm just not certain how to go about that.</p>
  
  <p>This jsbin <a href="http://jsbin.com/yaxame/1" rel="nofollow">http://jsbin.com/yaxame/1</a> shows the binding as a normal two way binding. Each time 'someone' 'isHappy' it alerts you that 'Someone is happy'. But I would like it to only alert when the data comes in from the api, and not the user input.</p>
  
  <p>two-way binding:</p>
  
  <pre><code>isHappyDidChange: function() {
    if (this.get('model.spouse.isHappy')) {
      alert('Someone is happy');
    }
  }.observes('model.spouse.isHappy')
  </code></pre>
  
  <p>I realize this jsbin <a href="http://jsbin.com/yaxame/2" rel="nofollow">http://jsbin.com/yaxame/2</a> is wrong as you need to trigger the binding template. So what is the correct way?</p>
  
  <p>one-way incorrect binding:</p>
  
  <pre><code>isHappyOneWay:  Ember.Binding.oneWay("model.spouse.isHappy"),
  
  isHappyDidChange: function() {
    if (this.get('model.spouse.isHappy')) {
      alert('Someone is happy');
    }
  }.observes('isHappyOneWay')
  </code></pre>
  
  <p><strong>Updated thought:</strong></p>
  
  <p>If I could just observe isLoaded like this:</p>
  
  <pre><code>isHappyDidChange: function() {
    if (this.get('model.spouse.isHappy')) {
      alert('Someone is happy');
    }
  }.observes('model.spouse.isLoaded')
  </code></pre>
  
  <p>Then that would be great, it might solve my problem. But the isLoaded doesn't actually mean the model is loaded... <a href="http://jsbin.com/yaxame/3" rel="nofollow">http://jsbin.com/yaxame/3</a></p>
  
  <p>Thanks!</p>