django/tests/modeltests/custom_managers/models.py

"""
23. Giving models a custom manager

You can use a custom ``Manager`` in a particular model by extending the base
``Manager`` class and instantiating your custom ``Manager`` in your model.

There are two reasons you might want to customize a ``Manager``: to add extra
``Manager`` methods, and/or to modify the initial ``QuerySet`` the ``Manager``
returns.
"""

from django.db import models

# An example of a custom manager called "objects".

class PersonManager(models.Manager):
    def get_fun_people(self):
        return self.filter(fun=True)

class Person(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    fun = models.BooleanField()
    objects = PersonManager()

    def __unicode__(self):
        return u"%s %s" % (self.first_name, self.last_name)

# An example of a custom manager that sets get_query_set().

class PublishedBookManager(models.Manager):
    def get_query_set(self):
        return super(PublishedBookManager, self).get_query_set().filter(is_published=True)

class Book(models.Model):
    title = models.CharField(max_length=50)
    author = models.CharField(max_length=30)
    is_published = models.BooleanField()
    published_objects = PublishedBookManager()
    authors = models.ManyToManyField(Person, related_name='books')

    def __unicode__(self):
        return self.title

# An example of providing multiple custom managers.

class FastCarManager(models.Manager):
    def get_query_set(self):
        return super(FastCarManager, self).get_query_set().filter(top_speed__gt=150)

class Car(models.Model):
    name = models.CharField(max_length=10)
    mileage = models.IntegerField()
    top_speed = models.IntegerField(help_text="In miles per hour.")
    cars = models.Manager()
    fast_cars = FastCarManager()

    def __unicode__(self):
        return self.name