title: differentiate polymorphic association type in views
body: <p>In my view I'm iterating through a list of messages which is a polymorphic association. I want to render different attributes from my polymorphic model (eg. Comment, Post) based on the polymorphic_type.</p>
  
  <p>How could this be handled in handlebars?</p>
  
  <pre><code>App.User = DS.Model.extend({
   messages: DS.hasMany(App.Message, {polymorphic: true})
  });
  
  App.Message = DS.Model.extend({
    created_at: DS.attr('date'),
    user: DS.belongsTo(App.User)
  });
  
  App.Post = App.Message.extend({
    title: DS.attr('string')
  });
  
  App.Comment = App.Message.extend({
    body: DS.attr('string'),
  });
  </code></pre>