Check If field exists in an sub-document of an Array

Question

I have a schema that is similar to this.

{id: Number,
  line_items: [{ 
    id: String,
    quantity: Number,
    revi         


        

Answer 1

let rankers = [
                    {
                        "_id": "5e4d4a13e0eb7b0733f27a18",
                        "totalMarks": 400,
                        "correct": 78,
                        "incorrect": 22,
                        "obtainMarks": 290,
                        "attemptCount": 100,
                        "timeTaken": 0,
                        "rank": 0,
                        "userRank": 1
                    },
                    {
                        "_id": "5e4d4a13e0eb7b0733f27a18",
                        "totalMarks": 400,
                        "correct": 77,
                        "incorrect": 21,
                        "obtainMarks": 287,
                        "attemptCount": 98,
                        "rank": 0,
                        "userRank": 2
                    },
                    {
                        "_id": "5e4d4a13e0eb7b0733f27a18",
                        "totalMarks": 400,
                        "correct": 76,
                        "incorrect": 21,
                        "obtainMarks": 283,
                        "attemptCount": 97,
                        "timeTaken": 0,
                        "userRank": 3
                    }
    ]

In the rankers collection rank and timeTaken key is missing in some documents so please

Results.aggregate([
{
    $project: {
        "totalMarks": 1,

        "correct": "$correct",
        "incorrect": "$incorrect",
        "obtainMarks": "$obtainMarks",
        "attemptCount": "$attemptCount",
        "timeTaken": {
            $cond: {
                if: { "$eq": [{ "$type": "$timeTaken" }, "missing"] },
                then: 0,
                else: "$timeTaken"
            }
        },
        "rank": {
            $cond: {
                if: { "$eq": [{ "$type": "$rank" }, "missing"] },
                then: 0,
                else: "$rank"
            }
        }
    }
}])