title: How to know if upsert was successful and if I can get _id of updated/new inserted document
body: <p>I am using this code to make upsert functiona to mongo server via mongoose</p>
  
  <pre><code>update({'name' : 'Jaki'}, {'name' : 'Charley', 'gender' : 'f'}, {upsert: true})
  </code></pre>
  
  <p>and it works, but how to know if operation was successful and if I can get <code>_id</code> of updated/new inserted document?
  (In sqlalchemy after session flush() I can get id of orm updated/inserted)</p>