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"""
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 __future__ import unicode_literals
from django.db import models
from django.utils.encoding import python_2_unicode_compatible
# An example of a custom manager called "objects".
class PersonManager(models.Manager):
def get_fun_people(self):
return self.filter(fun=True)
@python_2_unicode_compatible
class Person(models.Model):
first_name = models.CharField(max_length=30)
last_name = models.CharField(max_length=30)
fun = models.BooleanField()
objects = PersonManager()
def __str__(self):
return "%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)
@python_2_unicode_compatible
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 __str__(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)
@python_2_unicode_compatible
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 __str__(self):
return self.name
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