Any BSON value acceptable by mongodb as identifier
Sequence of operators specifying aggregate calculation.
Any BSON value acceptable by mongodb as identifier
Groups documents together to calulate aggregates on document collections. This command aggregates on arbitrary identifiers. Document fields identifier must be prefixed with
$. http://docs.mongodb.org/manual/reference/aggregation/group/#_S_groupAny BSON value acceptable by mongodb as identifier
Sequence of operators specifying aggregate calculation.