问题
I want to count all the numbers of different values in a field.there is no "annotate()" to use in mongoengine ,then how could i count the number and order them by numbers
The only way i thought out to solve this is use"distinct()"to find out the different values and then use "count()"to count each of the values it's a stupid way to realize the result i want
Do you have any other ways ?
回答1:
MongoEngine has some map reduce helpers that should meet your needs. The Queryset method item_frequencies[1] will meet your needs. There isnt any special support for the new aggregation framework but support could be added in the future.
Example usage:
BlogPost.objects.item_frequencies('tags')
[1] http://docs.mongoengine.org/en/latest/apireference.html?highlight=item_frequencies#mongoengine.queryset.QuerySet.item_frequencies
回答2:
MongoEngine itself has no special means to achieve this, but the MongoDB 2.2 aggregation framework lets you count documents, grouped by a field. I suggest using PyMongo's aggregate method directly with an aggregation pipeline to do this query:
http://api.mongodb.org/python/current/examples/aggregation.html
来源：https://stackoverflow.com/questions/13468687/mongoengine-django-how-to-count-the-number-of-items-of-same-content