find only specific inner array where condition match, ignroe other | MongoDB

In mongoose I am trying to fetch the inner record which match with specific condition. but it always return me both records, like it only treat the parent node rather than child.

$project aggregate function doesn't seems working as I expected `

[{
  "_id": {
    "$oid": "636b9958d6ea5d0cc85d20a6"
  },
  "project_type": 1,
  "title": "Pariatur Aut repreh",
  "id": 4,
  "drawings": [
    {
      "id": 1,
      "assigned_to": 4,
      "assigned_name": "Desirae Sandoval",
      "assigned_by": 3
    },
    {
      "id": 1,
      "assigned_to": 6,
      "assigned_name": "Desirae Sandoval",
      "assigned_by": 3
    }
  ],
  "status": 1,
  "created_at": {
    "$date": {
      "$numberLong": "1667995992724"
    }
  }
}]

I am expecting to get only that drawing which is assigned_to : 6
I have tried aggregate, match, project everything but none of them working, it always fetch both of the drawing, but I am expecting to fetch only one drawing 
This what I am expecting

    [{
  "_id": {
    "$oid": "636b9958d6ea5d0cc85d20a6"
  },
  "project_type": 1,
  "title": "Pariatur Aut repreh",
  "id": 4,
  "drawings": [
    {
      "id": 1,
      "assigned_to": 6,
      "assigned_name": "Desirae Sandoval",
      "assigned_by": 3
    }
  ],
  "status": 1,
  "created_at": {
    "$date": {
      "$numberLong": "1667995992724"
    }
  }
}]

CodePudding user response：

Use a filter

db.collection.aggregate([
  {
    $match: {
      "drawings.assigned_to": 6
    }
  },
  {
    $project: {
      project_type: 1,
      title: 1,
      id: 1,
      status: 1,
      created_at: 1,
      drawings: {
        $filter: {
          input: "$drawings",
          as: "drawings",
          cond: {
            $eq: [
              "$$drawings.assigned_to",
              6
            ]
          }
        }
      }
    }
  },
  
])

Edit: Add a match to remove all documents without any documents with any drawings.assigned_to of 6