author | Todd Larsen <tlarsen@google.com> |
Tue, 26 Aug 2008 21:49:54 +0000 | |
changeset 109 | 620f9b141567 |
permissions | -rwxr-xr-x |
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""" |
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23. Giving models a custom manager |
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You can use a custom ``Manager`` in a particular model by extending the base |
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``Manager`` class and instantiating your custom ``Manager`` in your model. |
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There are two reasons you might want to customize a ``Manager``: to add extra |
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``Manager`` methods, and/or to modify the initial ``QuerySet`` the ``Manager`` |
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returns. |
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""" |
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from django.db import models |
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# An example of a custom manager called "objects". |
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class PersonManager(models.Manager): |
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def get_fun_people(self): |
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return self.filter(fun=True) |
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class Person(models.Model): |
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first_name = models.CharField(maxlength=30) |
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last_name = models.CharField(maxlength=30) |
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fun = models.BooleanField() |
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objects = PersonManager() |
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def __str__(self): |
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return "%s %s" % (self.first_name, self.last_name) |
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# An example of a custom manager that sets get_query_set(). |
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class PublishedBookManager(models.Manager): |
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def get_query_set(self): |
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return super(PublishedBookManager, self).get_query_set().filter(is_published=True) |
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class Book(models.Model): |
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title = models.CharField(maxlength=50) |
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author = models.CharField(maxlength=30) |
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is_published = models.BooleanField() |
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published_objects = PublishedBookManager() |
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authors = models.ManyToManyField(Person, related_name='books') |
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def __str__(self): |
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return self.title |
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# An example of providing multiple custom managers. |
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class FastCarManager(models.Manager): |
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def get_query_set(self): |
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return super(FastCarManager, self).get_query_set().filter(top_speed__gt=150) |
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class Car(models.Model): |
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name = models.CharField(maxlength=10) |
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mileage = models.IntegerField() |
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top_speed = models.IntegerField(help_text="In miles per hour.") |
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cars = models.Manager() |
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fast_cars = FastCarManager() |
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def __str__(self): |
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return self.name |
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__test__ = {'API_TESTS':""" |
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>>> p1 = Person(first_name='Bugs', last_name='Bunny', fun=True) |
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>>> p1.save() |
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>>> p2 = Person(first_name='Droopy', last_name='Dog', fun=False) |
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>>> p2.save() |
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>>> Person.objects.get_fun_people() |
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[<Person: Bugs Bunny>] |
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# The RelatedManager used on the 'books' descriptor extends the default manager |
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>>> from modeltests.custom_managers.models import PublishedBookManager |
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>>> isinstance(p2.books, PublishedBookManager) |
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True |
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>>> b1 = Book(title='How to program', author='Rodney Dangerfield', is_published=True) |
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>>> b1.save() |
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>>> b2 = Book(title='How to be smart', author='Albert Einstein', is_published=False) |
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>>> b2.save() |
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# The default manager, "objects", doesn't exist, |
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# because a custom one was provided. |
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>>> Book.objects |
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Traceback (most recent call last): |
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... |
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AttributeError: type object 'Book' has no attribute 'objects' |
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# The RelatedManager used on the 'authors' descriptor extends the default manager |
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>>> from modeltests.custom_managers.models import PersonManager |
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>>> isinstance(b2.authors, PersonManager) |
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True |
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>>> Book.published_objects.all() |
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[<Book: How to program>] |
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>>> c1 = Car(name='Corvette', mileage=21, top_speed=180) |
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>>> c1.save() |
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>>> c2 = Car(name='Neon', mileage=31, top_speed=100) |
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>>> c2.save() |
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>>> Car.cars.order_by('name') |
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[<Car: Corvette>, <Car: Neon>] |
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>>> Car.fast_cars.all() |
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[<Car: Corvette>] |
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# Each model class gets a "_default_manager" attribute, which is a reference |
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# to the first manager defined in the class. In this case, it's "cars". |
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>>> Car._default_manager.order_by('name') |
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[<Car: Corvette>, <Car: Neon>] |
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"""} |