title: Transient and non-dirty attribute, ember-data
body: <p>I would like to declare transient attributes in my Ember models that doesn't affect the "dirty" state of the model.</p>
  
  <p>At the moment, I declare them like this within the model :</p>
  
  <pre><code>eventId: DS.attr("string", {defaultValue: "", transient: true})
  </code></pre>
  
  <p>They are ignored in the serializer, so they wont be posted to the API :</p>
  
  <pre><code>App.ApplicationSerializer = DS.RESTSerializer.extend({
      serializeAttribute: function(record, json, key, attribute) {
          if (attribute.options.transient) { return; }
          return this._super(record, json, key, attribute);
      }
  });
  </code></pre>
  
  <p>But the thing I also require that those properties doesn't change the "dirty" state of the object (for tracking and rollbacking without touching these).</p>