gistfile1.txt

{
            $match: {
                createdAt: {
                    $gte: fromDate.toISOString()
                }
            }
        },
        
        {
            "$project" :
            {
                _id : 0,
                "datePartDay" : {"$concat" : [
                    {"$substr" : [{"$dayOfMonth" : "$createdAt"}, 0, 2]}, "-",
                    {"$substr" : [{"$month" : "$createdAt"}, 0, 2]}, "-",
                    {"$substr" : [{"$year" : "$createdAt"}, 0, 4]}
                ] }
            }
        },

        {
            "$group" :
                { "_id" : "$datePartDay", "Count" : { "$sum" : 1 } }
        }