CODE EXAMPLE FOR JAVASCRIPT

query relation data in mongoose

var UserSchema = new mongoose.Schema({
    username: {
        type: String,
        index: true,
        required: true,
        unique: true
    },
    email: {
        type: String,
        required: true
    },
    password: {
        type: String,
        required: true
    },
    scores: [{ type: Schema.Types.ObjectId, ref: 'Score' }]
});

var GameSchema = new mongoose.Schema({
    name: String
});

var LobbySchema = new mongoose.Schema({
    _game: { 
       type: mongoose.Schema.Types.ObjectId, 
       ref: 'Game' 
     },
    name: String
});

var ScoreSchema = new mongoose.Schema({
    _user : { 
         type: mongoose.Schema.Types.ObjectId, 
         ref: 'User' 
       },
    _game : { 
         type: mongoose.Schema.Types.ObjectId, 
         ref: 'Game' 
       },
    score: Number
});


ScoreSchema.find({_id:##userIdHere##})
           .populate('_user')
           .populate('_game')  
           .exec(function(err, foundScore){
                   if(err){
                      res.send(err)
                    } else {
                 res.send(foundScore)
   }
}