best way of chaining mongoose queries
<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>