Populating nested properties with Mongoose - node.js

Question

In the API I'm trying to write with Node and Mongoose, the following query:
User.findOne({username: req.params.username}, "-_id -__v")
.populate({path: "songs", select: "-_id -__v"})
.populate({path: "following", select: "-_id username email"})
.exec(function(err, user) {
res.send(user);
});
returns the following JSON:
{
"email": "alice#alice.org",
"username": "alice",
"following": [
{
"username": "john",
"email": "john#john.org"
}
],
"songs": [
{
"slug": "dvorak-cello-concerto",
"artist": "5403e825cc9c45e9c55c4e7d",
"title": "Cello Concerto"
}
]
}
In the songs schema, I've setup artist as the following:
artist: {type: Schema.Types.ObjectId, ref: 'User'}
What is the best way to also populate the 'artist' property in every song that's populated in the initial query, rather than just its _id which references the user that song belongs to?

Answer 1

I figured out a way to do this, but please correct me if there's a better/cleaner way of doing it.
User.findOne({username: req.params.username}, "-_id -__v")
.populate({path: "songs", select: "-_id -__v"})
.exec(function(err, user) {
Songs.populate(user, {
path: 'songs.artist',
select: '-_id username',
model: 'User'
}, function (err, user) {
res.send(user);
});
});
Also, I'm only returning the 'username' value for the user which is all I need, but 'artist' still ends up being an object with that one property. If anybody knows how to return that value just as a string.
I'd love to know how.