Unable to perform complex nesting in mongodb queries?

Question

how to perform complete nesting in mongodbquery

Answer 1

There are many ways you can do this, here is an example by nesting $lookup's :

[
    {
        '$lookup': {
            'from': 'questionsanwereds',
            'let': {id: '$_id'},
            "pipeline": [
                {
                    $match: {
                        $expr: {
                            $eq: ["$$id", "$reqId"]
                        }
                    }
                },
                {
                    $unwind: "$questions"
                },
                {
                    $lookup: {
                        from: "questions",
                        localField: "questions.questionId",
                        foreignField: "_id",
                        as: "questionObj"
                    }
                },
                {
                    "$unwind": "$questionObj"
                },
                {
                    $group: {
                        _id: "$_id",
                        questions: {
                            $push: {
                                comment: "$comment",
                                name: "$questionObj.name",
                                optionSelected: "$optionSelected"
                            }
                        }
                    }
                }
            ],
            'as': 'questionsAnswereds'
        }
    },
    {
        '$unwind': {
            'path': '$questionsAnswereds'
        }
    }
]

The strategy is populating the name of each question separately and then grouping to restore the required structure.