108 lines
3.4 KiB
Python
108 lines
3.4 KiB
Python
"""
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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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"""}
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