chained model filters example

models.py

# an attempt to make filter, exclude, chainable
# based on: http://zmsmith.com/2010/04/using-custom-django-querysets/
# https://code.djangoproject.com/ticket/16748
# http://djangosnippets.org/snippets/734/


from django.db import models
from django.db.models.query import QuerySet
from datetime import date, timedelta

def manager(query_set_type):
    class QueryManager(models.Manager):
        def get_query_set(self):
            return query_set_type(self.model)

        def __getattr__(self, attr):
            if attr.startswith('_'):
                raise AttributeError(attr)
            return getattr(self.get_query_set(), attr)
    return QueryManager()

class ThoughtQuerySet(QuerySet):

    def useful(self):
        return self.filter(useful=True)

    def useless(self):
        return self.filter(useful=False)

    def new(self):
        return self.filter(created_on__gte=date.today())

    def recent(self):
        return self.filter(updated_on__gte=date.today() - timedelta(days=3))

class Thought(models.Model):
    subject = models.CharField(max_length=255)
    useful = models.BooleanField()
    created_on = models.DateField(auto_now_add=True)
    updated_on = models.DateField(auto_now=True)

    objects = manager(ThoughtQuerySet)