var GameSchema = new Schema({
    name: String,

    // one to one
    playerA: { type: mongoose.Schema.Types.ObjectId, ref: 'Player' },
    playerB: { type: mongoose.Schema.Types.ObjectId, ref: 'Player' },

    // one to many
    players: { type: [mongoose.Schema.Types.ObjectId], ref: 'Player' }
});

var PlayerSchema = new Schema({
  name: String,

  // hvis du også vil have en relation fra player til game:

  game: { type: mongoose.Schema.Types.ObjectId, ref: 'Game' }
});