title: best way of chaining mongoose queries
body: <p>I'm a novice developer using node and mongoose, and wondering what the best way of chaining queries with mongoose. I'm doing like below, it's not working.</p>
  
  <pre><code>User.findByIdAndUpdate(req.params._id, user, { upsert: true })
  .exec((err, updatedUser) =&gt; {
    if (addedCollections) {
      return User.findByIdAndUpdate(req.params._id, { $push: { _collections: { $each: addedCollections } } }, { upsert: true }).exec();
    }
    return new Query;
  })
  .exec(() =&gt; {
    return User.findById(req.params._id).populate('_collections');
  })
  .exec((err, user) =&gt; {
    res.json({ user });
  })
  </code></pre>
  
  <p>How can I do chain multiple queries?</p>