Improve performance aggregation count

[steevej (Steeve Juneau)]

@steevej

A slightly more complex alternative of the above would be to still use $sessioniControllo as the top input: but use the $cond expression (from the $filter) to only $add the matching jobId.

Basically, the top level $reduce $add (using $cond) 0 if the jobId does not match but $add the inner most $reduce if it does.

{
        $project: {
            "totale": {
                "$reduce": {
                    input: "$sessioniControllo" ,
                    initialValue: 0 ,
                    in: {
                        $add: [ "$$value",
                            { "cond" : [
                                { "$ne" : [ "$$this.jobId", Long("18453") ] } ,
                                0 ,
                                { "$reduce" : {
                                    input: "$$this.errori" ,
                                    initialValue: 0 ,
                                    in: {
                                        $add: [ "$$value" , { $size: "$$this.risultatoOperazione" } ]
                                    }
                                } }
                            ] } 
                        ]
                    }
                }
            }
        }
    }