How to use mongodb 'group' command in MongoEngine

[Raviteja]

Hi,

I haven't seen how to use mongodb 'group' command in the documentation.

Can anyone give me some insight?

Thanks,

Ravi

[JTG JTG]

A bit late, but may be useful for others :) Add mixin to your models:

class AdditionalMethods(object):

    @classmethod

    def aggregate(cls, pipeline):

        """

        Perform an aggregation using the aggregation framework on this collection.

        :param cls:

        :param pipeline: a single command or list of aggregation commands

        :return: PyMongo stuff (dict with "ok" and "result"...)

        """

        collection = _get_db()[cls._get_collection_name()]

        return collection.aggregate(pipeline)

    @classmethod

    def group(cls, key, condition, initial, reduce_f, finalize_f=None):

        """

        Perform a query.

        :param key: fields to group by

        :param condition: specification of rows to be considered (as a :meth:`find` query specification)

        :param initial: initial value of the aggregation counter object

        :param reduce_f: aggregation function as a JavaScript string

        :param finalize_f: function to be called on each object in output list

        :return: an array of grouped items

        """

        collection = _get_db()[cls._get_collection_name()]

        return collection.group(key, condition, initial, reduce_f, finalize_f)

This will allow you to call pyMongo methods indirectly:

        result = Product.group(key={'path': 1},

                               condition={"path": {"$in": [1,2,3]}},

                               initial={"products": [], "total": 0},

                               reduce_f="""

                                         function (curr, result) {

                                             result.products.push(curr.rn);

                                             result.total++;

                                         }""",

                               finalize_f=None)

          result = Product.aggregate([

                        { "$match":  {'path' : { '$in' : [self.rn] } } },

                        { "$group": {"_id": facets_all_group, "count": { "$sum" : 1 }} },

                        { "$sort": {"count":-1} }

                    ])['result']

http://api.mongodb.org/python/current/api/pymongo/collection.html#pymongo.collection.Collection.aggregate