title: Delete a key from a MongoDB document using Mongoose
body: <p>I'm using the <a href="https://github.com/LearnBoost/mongoose" rel="noreferrer">Mongoose</a> Library for accessing MongoDB with node.js</p>
  
  <p>Is there a way to <strong>remove a key from a document</strong>?  i.e. not just set the value to null, but remove it?</p>
  
  <pre><code>User.findOne({}, function(err, user){
    //correctly sets the key to null... but it's still present in the document
    user.key_to_delete = null;
  
    // doesn't seem to have any effect
    delete user.key_to_delete;
  
    user.save();
  });
  </code></pre>