Add a subdocument in array element

Question

Below function returns an array in 'results' argument:

module.exports.get = function (req, res) {
    objModel.find(function (err, results) {
        res.json({ record: results })
    })
};

I want to add its reference collection record list in one new object for each element. Just like the following:

for (var i = 0; i < results.length; i++) {
    module.exports.get = function (req, res) {
        objModel.find({ _id: results[i]._id }, function (err, record) {
            results[i]["objNew"] = record
        })
    };
}

My full code looks like:

module.exports.get = function (req, res) {
    objModel.find(function (err, results) {
        for (var i = 0; i < results.length; i++) {
            module.exports.get = function (req, res) {
                objModel.find({ _id: results[i]._id }, function (err, record) {
                    results[i]["objNew"] = record
                })
            };
        }
        res.json({ recordList: results })
    })
};

It return error: "objNew" is unknown.

I display output record json list in this link: Plunker

It would be very helpful if you could add extra bits in your question like your schema design, some sample documents and your expected JSON result example. — chridam
– chridam, Commented Jan 26, 2017 at 13:58
Apart from the fact that for loop is synchronous and it's iterating an asynchronous call (objModel.find(...)) you are bound to get incorrect results. — chridam
– chridam, Commented Jan 26, 2017 at 14:00

chridam · Accepted Answer · 2017-01-26 14:12:50Z

1

I believe you are after the $lookup operator in the aggregation framework which will give you the desired result. Consider running the following aggregate operation:

module.exports.get = function (req, res) {
    objModel.aggregate([
        {
            "$lookup": {
                "from": "objModelcollectionName", /* "self-join" with collection */
                "localField": "_id",
                "foreignField": "_id",
                "as": "objNew"
            }
        }
    ]).exec(function (err, results) {
        if (err) throw err;
        res.json({ recordList: results })
    })
};

answered Jan 26, 2017 at 14:12

chridam

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