Mongodb Query: Latest record by date for each item

Question

There are six devices 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

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.

Output is-

{
    "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
}

Thanks

Answer 2

use findOne instead of find Query db.collection.findOne({})