the $addToSet
expression
Represents one of the group/accumulator operators,
for the $group
aggregation.
Represents one of the group/accumulator operators,
for the $group
aggregation. Operation.
https://docs.mongodb.com/manual/reference/operator/aggregation/group/#accumulator-operator
the $max
expression
the $min
expression
the $push
expression
The $stdDevPop group accumulator (since MongoDB 3.2)
The $stdDevPop for a single field (since MongoDB 3.2)
The $stdDevSamp group accumulator (since MongoDB 3.2)
The $stdDevSamp for a single field (since MongoDB 3.2)
the $sum
expression
(Since version 0.12.0) Use SumAll
Factory to declare custom call to a group function.
Sum operation of the form $sum: 1