title: MongoDB Add extra embedded document instead of overwriting it
body: <p>I have a MongoDocument X which has some instances of MongoEmbeddedDocument Y.</p>
  
  <p>I now want to add an extra embeddeddocument Y to my X collection. I've tried the following code:</p>
  
  <pre><code>var mongo = db.x.findOne();
  mongo.y = { title:"test" }
  db.x.save(mongo)
  </code></pre>
  
  <p>The problem is that that piece of code will deleted my entire collection of y embeddeddocuments that I had. Is there someway I can add one without deleting the existing ones?</p>