Mongoose Aggregate : limit the number of records in $group

Question

I am trying to convert this sentence using the Mongoose Aggregate method :

\"For each player with given oid, select the game that has been played the most\". Here is my

Answer 1

You can use $first to take values from the first doc in each group of a sorted pipeline:

var allids = ['xxxxx','yyyy'];
Game.aggregate([
    {$match: {'oid': {$in:allids}}},
    {$sort: {'number_plays': -1}},
    {$group: {
        _id: '$oid', 
        game_name: {$first: "$game_name"}, 
        game_id: {$first: "$game_id"}, 
        number_plays: {$first:"$number_plays"}
    }}
], function(err,list){
    console.log(list);
    res.end();
});

Because you've sorted on number_plays descending in the preceding stage of the pipeline, this will take the values from each oid group's doc with the highest number_plays.