nested_populate.js

router.get('/carlos', (req, res, next) => {
  Post.find().populate('creator').populate({
    path:'comments',
    populate:{
      path:'author',
      model:'User'
    }
  })
  .then(posts => {
    res.send(posts);
  })
  .catch(err => {
    res.send(err);
  })
});