title: trigging after_save on an embedded item when assigning it via '<<' in mongoid?
body: <p>I was wondering if there was a way to trigger the after_save callback on an embedded_in object in Mongoid mapper.</p>
  
  <p>Example:</p>
  
  <pre><code>i = Image.new(:file =&gt; file)
  user.images &lt;&lt; i
  # =&gt; i.after_save should be triggered here
  </code></pre>
  
  <p>I'm aware that if I call <code>i.save</code> after words, it will fire, however really hard to remember to do that throughout my code.</p>
  
  <p>Also, calling <code>user.images.create(:file =&gt; file)</code> is not an option, because I do a check to make sure the same file isn't uploaded twice.</p>