Question 348382 in Mongodb Question posted in
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Mongodb – Mongo aggregation project arrays intersection

I have a collection of documents where each of the documents may have an array of teamsIds like:

{
  "id": 1,
  "teamsIds": ["team_a", "team_b"]
}

I’m trying to write an Aggregation (doing $match stage before) that will $project the documents and return objects like:

{ 
  "id": 1,
  "matchingFilter": true
}

where matchingFilter should be true when teamsIds does contain any of the teams I’m checking for. In the case of the document above, I need matchingFilter to be true when searching for teams: ["team_c", "team_a"] because it has assigned "team_a". What would be the simplest way to achieve it? I can’t use $elemMatch in the Aggregation pipeline, is there an equivalent I could use?

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2

Answers


  1. 0

    You can use $match to look for documents that have a teamsIds element value $in a user supplied array of values then just $set the matchingFilter: true to all matching document like so:

    db.collection.aggregate([
  {
    $match: {
      teamsIds: {
        $in: [
          "team_a",
          "team_c"
        ]
      }
    }
  },
  {
    $set: {
      matchingFilter: true
    }
  },
  {
    $project: {
      _id: 0,
      id: 1,
      matchingFilter: 1
    }
  }
])

    See HERE for a working example.

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  2. 0

    The canonical implementation of your expected set intersection behaviour is using $setIntersection

    db.collection.aggregate([
  {
    "$match": {
      // your match here
      
    }
  },
  {
    "$project": {
      "id": 1,
      "matchingFilter": {
        "$ne": [
          [],
          {
            "$setIntersection": [
              "$teamsIds",
              // your input array here
              [
                "team_c",
                "team_a"
              ]
            ]
          }
        ]
      }
    }
  }
])

    Mongo Playground

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