I'm saving data for a NestJs based web app in MongoDB.

My MongoDB Data looks like this

"gameId": "1a2b3c4d5e"
"rounds": [
    {
      "matches": [
        {
          "match_id": "1111abc1111",
          "team1": {
            "team_id": "team8",
            "score": 0
          },
          "team2": {
            "team_id": "team2",
            "score": 0
          }
        },
        {
          "match_id": "2222abc2222",
          "team1": {
            "team_id": "team6",
            "score": 0
          },
          "team2": {
            "team_id": "team5",
            "score": 0
          }
        },
      ]
    }
  ]

Here we have gameId for each game and inside each game, there are many rounds and many matches. Each match has match_id. How can I get a particular match info and edit it based on gameId & match_id? (N.B: I'm willing to update score based on match_id)

I've tried something like this

    const matchDetails = await this.gameModel.findOne({
      gameId: gameId,
      rounds: { $elemMatch: { match_id: match_id } },
    });

But this doesn't work and returns null. How to do this correctly?

CodePudding user response：

The problem is that you're applying the elemMatch on the rounds array, but it should be on rounds.matches. Changing your query to the following will fix the problem:

const matchDetails = await this.gameModel.findOne({
      gameId: gameId,
      "rounds.matches": { $elemMatch: { match_id: match_id } },
});

EDIT: To only get a specific matching element, you can use a simple aggregation with $unwind and $filter:

db.collection.aggregate([
  {
    "$match": {
      "gameId": gameId,
      "rounds.matches": { $elemMatch: { match_id: match_id } }
    }
  },
  {
    "$unwind": "$rounds"
  },
  {
    $project: {
      match: {
        $filter: {
          input: "$rounds.matches",
          as: "match",
          cond: {
            $eq: [
              "$$match.match_id",
              match_id 
            ]
          }
        }
      },
      _id: 0
    }
  }
])

Example on mongoplayground.