title: How to perform operation on subdocuments without fetching a parent in Mongoose?
body: <p>For now in case I want to remove a subdocument I do this:</p>
  
  <pre><code>Post.findById(post_id).exec(function(err, post) {
    post.comments.remove({'_id': comment_id});
    post.save(function(err) {
      res.end("Hooray!");
    });
  });
  </code></pre>
  
  <p>Which seem to be non-optimal to me, because each time I remove a comment the whole post will be fetched from DB and it has a lot of stuff attached to it. So, is it possible to modify subdocuments without fetching a parent document?</p>