Latest record by date for each item mongodb group

Question

There are many items in a collection, each has many records, some have records of new dates and some have week or/and month older. I need a query which returns latest last record of each item. In the case of .aggregate() I need that complete "data" filed. I want this result using mongodb $group, the record should be latest for each device.

   {
    "result" : [ 
        {
            "_id" : 29,
            "gateway_id" : 1,
            "data" : [ 
                {
                    "r" : 203,
                    "v" : 3002
                }, 
                {
                    "r" : 221,
                    "v" : 3006
                }
            ],
            "device_id" : 29,
            "date_time" : "a"
        }, 
        {
            "_id" : 28,
            "gateway_id" : 1,
            "data" : [ 
                {
                    "r" : 203,
                    "v" : 3002
                }, 
                {
                    "r" : 221,
                    "v" : 3006
                }
            ],
            "device_id" : 28,
            "date_time" : "b"
        }, 
        {
            "_id" : 27,
            "gateway_id" : 1,
            "data" : [ 
                {
                    "r" : 203,
                    "v" : 3642
                }, 
                {
                    "r" : 221,
                    "v" : 3666
                }
            ],
            "device_id" : 27,
            "date_time" : "a"
        }
    ],
    "ok" : 1
}

I want this result using mongodb $group, the record should be latest for each device.

Answer 1

Try with following snippet

db.collection.aggregate([
    {$group: {
        "_id": "$device_id",
        "gateway_id": {"$last":"$gateway_id"},
        "data": {"$last": '$data'},
        "date": {"$last": '$date_time'},
    }},
    {$project: {
        "device_id": "$_id",
        "gateway_id": "$gateway_id",
        "data": "$data",
        "date_time": "$date"
    }},
    {$sort: {
        "date": -1
    }}
]);

In above query group by device id and date, data, and gateway_id will be latest in each row.