This is just a quick how-to on creating a custom manager for a MongoEngine Model in Django, similar to how you would normally create a Manager for a Model in Django. Usually in Django with a PostgreSQL or MySQL database, one would do this:

class PollManager(models.Manager):
    def with_counts(self):
        ...

class OpinionPoll(models.Model):
    question = models.CharField(max_length=200)
    poll_date = models.DateField()
    objects = PollManager()

Now, when we are using Mongoengine Documents, it works only slightly differently, and you just need to know how (since this doesn't seem to be documented anywhere). This is how I do it:

from mongoengine import *
from mongoengine.queryset import QuerySet

class PollManager(QuerySet):
    def __init__(self, document, collection, *args, **kwargs)
       super(PollManager, self).__init__(document, collection, *args, **kwargs)
    def with_counts(self):
       ...

class OpinionPoll(Document):
    question = StringField(max_length=200)
    poll_date = DateTimeField()

OpinionPoll.add_to_class('objects', PollManager(OpinionPoll, 
               OpinionPoll.objects._collection))

You might notice that the last line contains what developers often refer to as "monkey patching", adding something to a class after it was defined. In this case, however, it is a necessary evil, since we need to be able to access the OpinionPoll class to instantiate the manager. Maybe there's a better way, and if so I'll be happy to hear about it. Left as an exercise for the reader, as they say!