Group documents by value from another field

Question

I have documents in the format of

{
    "_id": <some_id>,
    "code": <some_code>,
    "manually_updated": {
        "code": <some_code>
    }
}

I would like to find duplicates (group documents) by looking into root code value but also in manually_updated.code field. So the following three documents would be seen as duplicates (second document code was "overwritten" by adding the code to manually_updated with the same code as the first and third document):

{
    {
        "_id" : ObjectId("5d2dc168651ce400a327b408"),
        "code": 'ABCD',
        "manually_updated": {}
    },
    {
        "_id" : ObjectId("5d40861411981f0068e22511"),
        "code": 'EFGH',
        "manually_updated": {
            "code": "ABCD"
        }
    },
    {
        "_id" : ObjectId("5d41374311981f0163779b79"),
        "code": 'ABCD',
        "manually_updated": {}
    }
}

Thank you.

Answer 1

Please try this :

    db.getCollection('yourCollection').aggregate([{
    $lookup:
    {
        from: "yourCollection",
        let: { codeToBeCompared: "$code", manualCode: '$manually_updated.code' },
        pipeline: [
            {
                $match:
                {
                    $expr:
                    {

                        $or:
                            [
                                { $eq: ["$code", "$$codeToBeCompared"] },
                                { $eq: ["$manually_updated.code", "$$codeToBeCompared"] },
                                { $and: [{ $gt: ['$manually_updated', {}] }, { $eq: ["$manually_updated.code", '$$manualCode'] }] }
                            ]
                    }
                }
            }

        ],
        as: "data"
    }
}, { $group: { _id: '$code', manually_updated: { $push: '$manually_updated' }, finalData: { $first: '$$ROOT' } } }, { $match: { $expr: { $gt: [{ $size: "$finalData.data" }, 1] } } },
   { $project: { 'manually_updated': 1, 'data': '$finalData.data' } }])

Sample Docs :

/* 1 */
{
    "_id" : ObjectId("5d2dc168651ce400a327b408"),
    "code" : "ABCD",
    "manually_updated" : {}
}

/* 2 */
{
    "_id" : ObjectId("5d40861411981f0068e22511"),
    "code" : "EFGH",
    "manually_updated" : {
        "code" : "ABCD"
    }
}

/* 3 */
{
    "_id" : ObjectId("5d41374311981f0163779b79"),
    "code" : "ABCD",
    "manually_updated" : {}
}

/* 4 */
{
    "_id" : ObjectId("5d518a3ce8078d6134c4cd21"),
    "code" : "APPPP",
    "manually_updated" : {}
}

/* 5 */
{
    "_id" : ObjectId("5d518a3ce8078d6134c4cd22"),
    "code" : "APPPP",
    "manually_updated" : {
        "code" : "ABCD"
    }
}

/* 6 */
{
    "_id" : ObjectId("5d518a3ce8078d6134c4cd23"),
    "code" : "APPPP",
    "manually_updated" : {}
}

/* 7 */
{
    "_id" : ObjectId("5d518a3ce8078d6134c4cd24"),
    "code" : "deffffff",
    "manually_updated" : {}
}

Output :

/* 1 */
{
    "_id" : "APPPP",
        "manually_updated" : [ // Preserving this to say we've passed thru these values
            {},
            {
                "code": "ABCD"
            },
            {}
        ],
            "data" : [
                {
                    "_id": ObjectId("5d518a3ce8078d6134c4cd21"),
                    "code": "APPPP",
                    "manually_updated": {}
                },
                {
                    "_id": ObjectId("5d518a3ce8078d6134c4cd22"),
                    "code": "APPPP",
                    "manually_updated": {
                        "code": "ABCD"
                    }
                },
                {
                    "_id": ObjectId("5d518a3ce8078d6134c4cd23"),
                    "code": "APPPP",
                    "manually_updated": {}
                }
            ]
}

/* 2 */
{
    "_id" : "EFGH",
        "manually_updated" : [
            {
                "code": "ABCD"
            }
        ],
            "data" : [
                {
                    "_id": ObjectId("5d40861411981f0068e22511"),
                    "code": "EFGH",
                    "manually_updated": {
                        "code": "ABCD"
                    }
                }
            ]
}

/* 3 */
{
    "_id" : "ABCD",
        "manually_updated" : [
            {},
            {}
        ],
            "data" : [
                {
                    "_id": ObjectId("5d2dc168651ce400a327b408"),
                    "code": "ABCD",
                    "manually_updated": {}
                },
                {
                    "_id": ObjectId("5d40861411981f0068e22511"),
                    "code": "EFGH",
                    "manually_updated": {
                        "code": "ABCD"
                    }
                },
                {
                    "_id": ObjectId("5d41374311981f0163779b79"),
                    "code": "ABCD",
                    "manually_updated": {}
                },
                {
                    "_id": ObjectId("5d518a3ce8078d6134c4cd22"),
                    "code": "APPPP",
                    "manually_updated": {
                        "code": "ABCD"
                    }
                }
            ]
}

Also this does scan on everything, you can have $match as first stage to filter documents based on a particular code.