Multiple nested grouping in MongoDB Aggregation - mongodb

Question

I have more than thousand of documents in my mongoDB collection where each document represents the data for a song like this:
{
"_id": ObjectID("612e03a790c3d3189845589b"),
"artist": "3 Doors Down",
"title": "Landning in London",
"album": "Another 700 Miles",
"genre": "Seventeen Days",
"trackNumber": 5,
"year": 2005,
"rating": 3,
"duration": "4:32",
"country": "United States",
}
Now with the help of the aggregation pipeline I want to group my collections the following way. So Far I could do grouping for 1 stage but I struggle to push through the complete root document until end and do this nested grouping.
List all genres --> list all artists within this genre --> list all albums of this artist within this genre --> list the COMPLETE root document for all songs of this album:
{
[
{
"genreName": "Alternative Rock",
"artists": [
{
"artistName": "3 Doors Down",
"albums": [
{
"albumName": "Seventeen Days",
"songs": [
{
"_id": ObjectID(612e03a790c3d3189845589b),
"artist": "3 Doors Down",
"title": "Landning in London",
"album": "Another 700 Miles",
"genre": "Seventeen Days",
"trackNumber": 5,
"year": 2005,
"rating": 3,
"duration": "4:32",
"country": "United States",
}
]
}
]
}
]
}
]
}

Answer 1

This one should work:
db.collection.aggregate([
{
$group: {
_id: { genreName: "$genre", artistName: "$artist", albumName: "$album" },
songs: { $push: "$$ROOT" }
}
},
{
$group: {
_id: { genreName: "$_id.genreName", artistName: "$_id.artistName" },
albums: { $push: { albumName: "$_id.albumName", songs: "$songs" } }
}
},
{
$group: {
_id: "$_id.genreName",
artists: { $push: { artistsName: "$_id.artistsName", albums: "$albums" } }
}
},
{ $project: { _id: 0, genreName: "$_id", artists: 1 } }
])