Django has out-of-the-box support for aggregation. The following aggregations are currently supported by Django MongoDB Engine:
While being more flexible than Map/Reduce, a
group command can not be
processed in parallel, for which reason you should prefer Map/Reduce to process
big data sets.
Needless to say, you shouldn’t use these aggregations on a regular basis (i.e. in your views or business logic) but regard them as a powerful tool for one-time operations.