aggregate_sum/average + unit tests

mongoengine/queryset/base.py

@@ -1248,6 +1248,23 @@ class BaseQuerySet(object):
         else:
             return 0
 
+    def aggregate_sum(self, field):
+        """Sum over the values of the specified field.
+
+        :param field: the field to sum over; use dot-notation to refer to
+            embedded document fields
+
+        This method is more performant than the regular `sum`, because it uses
+        the aggregation framework instead of map-reduce.
+        """
+        result = self._document._get_collection().aggregate([
+            { '$match': self._query },
+            { '$group': { '_id': 'sum', 'total': { '$sum': '$' + field } } }
+        ])
+        if result['result']:
+            return result['result'][0]['total']
+        return 0
+
     def average(self, field):
         """Average over the values of the specified field.
 
@@ -1303,6 +1320,23 @@ class BaseQuerySet(object):
         else:
             return 0
 
+    def aggregate_average(self, field):
+        """Average over the values of the specified field.
+
+        :param field: the field to average over; use dot-notation to refer to
+            embedded document fields
+
+        This method is more performant than the regular `average`, because it
+        uses the aggregation framework instead of map-reduce.
+        """
+        result = self._document._get_collection().aggregate([
+            { '$match': self._query },
+            { '$group': { '_id': 'avg', 'total': { '$avg': '$' + field } } }
+        ])
+        if result['result']:
+            return result['result'][0]['total']
+        return 0
+
     def item_frequencies(self, field, normalize=False, map_reduce=True):
         """Returns a dictionary of all items present in a field across
         the whole queried set of documents, and their corresponding frequency.