Btukfyl

sin my MongoDB I have documents like this:

{

    "_id" : ObjectId("5bf3cd1c6b86db2c84d"),

    "_class" : "Log",

    "data" : {

        "devices" : [ 

             {

                "id": "12364",

        "name":"name"

             }, 

             {

                "id": "12346",

        "name":"name"

            }, 

            {

                "id": "12345",

        "name":"name"

            }

        ]

    }

}

I wanted to return number of devices, so I created query:

db.getCollection('coll').aggregate(

{$group: { _id: null, totalSize: { $sum: { $size: "$data.devices"}} }})

which returns me:

{ "_id" : null, "totalSize" : 6 }

But how to create method to return "totalSize" in Spring Data?

I get stuck and I dont know how to solve it:

public Long countDevices() {

        GroupOperation groupOperation= Aggregation.group("_id").sum("_id");



        Aggregation aggregation = Aggregation.newAggregation(groupOperation);



        mongoOperations.aggregate(matchOperation,)



        return ...

    }

below solution seems to work, but its not looks so pretty and performance:

public Long count(Criteria searchCriteria) {



     Aggregation aggregation = Aggregation.newAggregation(

             Aggregation.match(searchCriteria),

             Aggregation.unwind("data.device")

     );

        AggregationResults aggregationResults = mongoOperations.aggregate(aggregation,"coll", DBObject.class);

        return (long) aggregationResults.getMappedResults().size();



    }