Add field to every object in array of objects in mongo aggregation

Question

I have one field in schema at root level and want to add it in every object from array which matches a condition.

Here is a sample document....

{
    calls: [
      {
        "name": "sam",
        "status": "scheduled"
      },
      {
        "name": "tom",
        "status": "cancelled"
      },
      {
        "name": "bob",
        "status": "scheduled"
      },
      
    ],
    "time": 1620095400000.0,
    "call_id": "ABCABCABC"
}

Required document is as follows:

[
  {
    "call_id": "ABCABCABC",
    "calls": [
      {
        "call_id": "ABCABCABC",
        "name": "sam",
        "status": "scheduled"
      },
      {
        "name": "tom",
        "status": "cancelled"
      },
      {
        "call_id": "ABCABCABC",
        "name": "bob",
        "status": "scheduled"
      }
    ],
    "time": 1.6200954e+12
  }
]

The call_id should be added to all objects in array whose status is "scheduled". Is it possible to do this with mongo aggregation? I have tried $addFields but was unable to achieve above result. Thanks in advance!

Answer 1

Here is how I would do it using $map and $mergeObjects

db.collection.aggregate([
  {
    "$addFields": {
      calls: {
        $map: {
          input: "$calls",
          as: "call",
          in: {
            $cond: [
              {
                $eq: [
                  "$$call.status",
                  "scheduled"
                ]
              },
              {
                "$mergeObjects": [
                  "$$call",
                  {
                    call_id: "$call_id"
                  }
                ]
              },
              "$$call"
            ]
          }
        }
      }
    }
  }
])

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