the name of the output field which has the count as its value
(count: StringAdd).self
(count: StringFormat).self
(count: ArrowAssoc[Count]).x
(Since version 2.10.0) Use leftOfArrow
instead
(count: Ensuring[Count]).x
(Since version 2.10.0) Use resultOfEnsuring
instead
_Since MongoDB 3.4:_ Counts of the number of documents input. https://docs.mongodb.com/manual/reference/operator/aggregation/count/
the name of the output field which has the count as its value