MongoDB:Mappa kapslad array i aggregatfunktion

Detta borde fungera.

{
    $addFields: {
        "payLoad.grades": {
            $map: {
                input: "$payLoad.grades",
                as: "grade",
                in: {
                    grade: "$$grade.grade_",
                    mean: "$$grade.mean"
                }
            }
        }
    }
}