Add missing imports and models to the examples in the the model layer documentation
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@ -97,6 +97,8 @@ second element is the human-readable name. For example::
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Generally, it's best to define choices inside a model class, and to
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define a suitably-named constant for each value::
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from django.db import models
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class Student(models.Model):
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FRESHMAN = 'FR'
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SOPHOMORE = 'SO'
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@ -994,12 +996,15 @@ relationship with itself -- use ``models.ForeignKey('self')``.
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If you need to create a relationship on a model that has not yet been defined,
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you can use the name of the model, rather than the model object itself::
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from django.db import models
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class Car(models.Model):
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manufacturer = models.ForeignKey('Manufacturer')
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# ...
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class Manufacturer(models.Model):
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# ...
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pass
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To refer to models defined in another application, you can explicitly specify
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a model with the full application label. For example, if the ``Manufacturer``
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@ -1132,6 +1137,9 @@ The possible values for :attr:`~ForeignKey.on_delete` are found in
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necessary to avoid executing queries at the time your models.py is
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imported::
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from django.db import models
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from django.contrib.auth.models import User
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def get_sentinel_user():
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return User.objects.get_or_create(username='deleted')[0]
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@ -1204,6 +1212,8 @@ that control how the relationship functions.
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Only used in the definition of ManyToManyFields on self. Consider the
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following model::
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from django.db import models
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class Person(models.Model):
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friends = models.ManyToManyField("self")
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@ -34,6 +34,8 @@ that, you need to :meth:`~Model.save()`.
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1. Add a classmethod on the model class::
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from django.db import models
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class Book(models.Model):
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title = models.CharField(max_length=100)
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@ -105,6 +107,7 @@ individually.
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You'll need to call ``full_clean`` manually when you want to run one-step model
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validation for your own manually created models. For example::
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from django.core.exceptions import ValidationError
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try:
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article.full_clean()
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except ValidationError as e:
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@ -132,6 +135,7 @@ automatically provide a value for a field, or to do validation that requires
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access to more than a single field::
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def clean(self):
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import datetime
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from django.core.exceptions import ValidationError
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# Don't allow draft entries to have a pub_date.
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if self.status == 'draft' and self.pub_date is not None:
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@ -434,6 +438,8 @@ representation of the model from the ``__unicode__()`` method.
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For example::
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from django.db import models
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class Person(models.Model):
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first_name = models.CharField(max_length=50)
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last_name = models.CharField(max_length=50)
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@ -460,6 +466,9 @@ Thus, you should return a nice, human-readable string for the object's
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The previous :meth:`~Model.__unicode__()` example could be similarly written
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using ``__str__()`` like this::
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from django.db import models
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from django.utils.encoding import force_bytes
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class Person(models.Model):
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first_name = models.CharField(max_length=50)
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last_name = models.CharField(max_length=50)
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@ -490,6 +499,7 @@ function is usually the best approach.)
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For example::
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def get_absolute_url(self):
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from django.core.urlresolvers import reverse
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return reverse('people.views.details', args=[str(self.id)])
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One place Django uses ``get_absolute_url()`` is in the admin app. If an object
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@ -145,6 +145,12 @@ Django quotes column and table names behind the scenes.
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and a question has more than one answer, and the order of answers matters, you'd
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do this::
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from django.db import models
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class Question(models.Model):
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text = models.TextField()
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# ...
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class Answer(models.Model):
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question = models.ForeignKey(Question)
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# ...
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@ -232,6 +232,7 @@ the model field that is being aggregated.
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For example, if you were manipulating a list of blogs, you may want
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to determine how many entries have been made in each blog::
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>>> from django.db.models import Count
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>>> q = Blog.objects.annotate(Count('entry'))
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# The name of the first blog
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>>> q[0].name
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@ -699,6 +700,8 @@ And here's ``select_related`` lookup::
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``select_related()`` follows foreign keys as far as possible. If you have the
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following models::
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from django.db import models
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class City(models.Model):
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# ...
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pass
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@ -814,6 +817,8 @@ that are supported by ``select_related``. It also supports prefetching of
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For example, suppose you have these models::
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from django.db import models
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class Topping(models.Model):
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name = models.CharField(max_length=30)
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@ -1565,6 +1570,7 @@ aggregated.
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For example, when you are working with blog entries, you may want to know the
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number of authors that have contributed blog entries::
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>>> from django.db.models import Count
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>>> q = Blog.objects.aggregate(Count('entry'))
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{'entry__count': 16}
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@ -2042,6 +2048,7 @@ Range test (inclusive).
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Example::
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import datetime
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start_date = datetime.date(2005, 1, 1)
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end_date = datetime.date(2005, 3, 31)
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Entry.objects.filter(pub_date__range=(start_date, end_date))
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@ -12,8 +12,11 @@ Related objects reference
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* The "other side" of a :class:`~django.db.models.ForeignKey` relation.
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That is::
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from django.db import models
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class Reporter(models.Model):
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...
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# ...
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pass
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class Article(models.Model):
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reporter = models.ForeignKey(Reporter)
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@ -24,7 +27,8 @@ Related objects reference
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* Both sides of a :class:`~django.db.models.ManyToManyField` relation::
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class Topping(models.Model):
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...
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# ...
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pass
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class Pizza(models.Model):
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toppings = models.ManyToManyField(Topping)
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@ -18,27 +18,29 @@ used to track the inventory for a series of online bookstores:
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.. code-block:: python
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from django.db import models
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class Author(models.Model):
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name = models.CharField(max_length=100)
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age = models.IntegerField()
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name = models.CharField(max_length=100)
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age = models.IntegerField()
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class Publisher(models.Model):
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name = models.CharField(max_length=300)
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num_awards = models.IntegerField()
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name = models.CharField(max_length=300)
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num_awards = models.IntegerField()
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class Book(models.Model):
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name = models.CharField(max_length=300)
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pages = models.IntegerField()
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price = models.DecimalField(max_digits=10, decimal_places=2)
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rating = models.FloatField()
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authors = models.ManyToManyField(Author)
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publisher = models.ForeignKey(Publisher)
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pubdate = models.DateField()
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name = models.CharField(max_length=300)
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pages = models.IntegerField()
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price = models.DecimalField(max_digits=10, decimal_places=2)
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rating = models.FloatField()
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authors = models.ManyToManyField(Author)
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publisher = models.ForeignKey(Publisher)
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pubdate = models.DateField()
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class Store(models.Model):
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name = models.CharField(max_length=300)
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books = models.ManyToManyField(Book)
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registered_users = models.PositiveIntegerField()
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name = models.CharField(max_length=300)
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books = models.ManyToManyField(Book)
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registered_users = models.PositiveIntegerField()
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Cheat sheet
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===========
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@ -123,7 +125,7 @@ If you want to generate more than one aggregate, you just add another
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argument to the ``aggregate()`` clause. So, if we also wanted to know
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the maximum and minimum price of all books, we would issue the query::
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>>> from django.db.models import Avg, Max, Min, Count
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>>> from django.db.models import Avg, Max, Min
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>>> Book.objects.aggregate(Avg('price'), Max('price'), Min('price'))
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{'price__avg': 34.35, 'price__max': Decimal('81.20'), 'price__min': Decimal('12.99')}
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@ -148,6 +150,7 @@ the number of authors:
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.. code-block:: python
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# Build an annotated queryset
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>>> from django.db.models import Count
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>>> q = Book.objects.annotate(Count('authors'))
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# Interrogate the first object in the queryset
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>>> q[0]
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@ -192,6 +195,7 @@ and aggregate the related value.
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For example, to find the price range of books offered in each store,
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you could use the annotation::
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>>> from django.db.models import Max, Min
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>>> Store.objects.annotate(min_price=Min('books__price'), max_price=Max('books__price'))
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This tells Django to retrieve the ``Store`` model, join (through the
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@ -222,7 +226,7 @@ For example, we can ask for all publishers, annotated with their respective
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total book stock counters (note how we use ``'book'`` to specify the
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``Publisher`` -> ``Book`` reverse foreign key hop)::
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>>> from django.db.models import Count, Min, Sum, Max, Avg
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>>> from django.db.models import Count, Min, Sum, Avg
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>>> Publisher.objects.annotate(Count('book'))
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(Every ``Publisher`` in the resulting ``QuerySet`` will have an extra attribute
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@ -269,6 +273,7 @@ constraining the objects for which an annotation is calculated. For example,
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you can generate an annotated list of all books that have a title starting
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with "Django" using the query::
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>>> from django.db.models import Count, Avg
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>>> Book.objects.filter(name__startswith="Django").annotate(num_authors=Count('authors'))
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When used with an ``aggregate()`` clause, a filter has the effect of
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@ -407,6 +412,8 @@ particularly, when counting things.
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By way of example, suppose you have a model like this::
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from django.db import models
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class Item(models.Model):
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name = models.CharField(max_length=10)
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data = models.IntegerField()
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@ -457,5 +464,6 @@ For example, if you wanted to calculate the average number of authors per
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book you first annotate the set of books with the author count, then
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aggregate that author count, referencing the annotation field::
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>>> from django.db.models import Count, Avg
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>>> Book.objects.annotate(num_authors=Count('authors')).aggregate(Avg('num_authors'))
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{'num_authors__avg': 1.66}
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@ -62,6 +62,8 @@ For example, this custom ``Manager`` offers a method ``with_counts()``, which
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returns a list of all ``OpinionPoll`` objects, each with an extra
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``num_responses`` attribute that is the result of an aggregate query::
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from django.db import models
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class PollManager(models.Manager):
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def with_counts(self):
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from django.db import connection
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@ -101,6 +103,8 @@ Modifying initial Manager QuerySets
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A ``Manager``'s base ``QuerySet`` returns all objects in the system. For
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example, using this model::
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from django.db import models
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class Book(models.Model):
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title = models.CharField(max_length=100)
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author = models.CharField(max_length=50)
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@ -236,7 +240,7 @@ class, but still customize the default manager. For example, suppose you have
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this base class::
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class AbstractBase(models.Model):
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...
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# ...
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objects = CustomManager()
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class Meta:
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@ -246,14 +250,15 @@ If you use this directly in a subclass, ``objects`` will be the default
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manager if you declare no managers in the base class::
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class ChildA(AbstractBase):
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...
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# ...
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# This class has CustomManager as the default manager.
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pass
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If you want to inherit from ``AbstractBase``, but provide a different default
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manager, you can provide the default manager on the child class::
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class ChildB(AbstractBase):
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...
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# ...
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# An explicit default manager.
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default_manager = OtherManager()
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@ -274,9 +279,10 @@ it into the inheritance hierarchy *after* the defaults::
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abstract = True
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class ChildC(AbstractBase, ExtraManager):
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...
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# ...
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# Default manager is CustomManager, but OtherManager is
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# also available via the "extra_manager" attribute.
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pass
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Note that while you can *define* a custom manager on the abstract model, you
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can't *invoke* any methods using the abstract model. That is::
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@ -349,8 +355,7 @@ the manager class::
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class MyManager(models.Manager):
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use_for_related_fields = True
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...
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# ...
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If this attribute is set on the *default* manager for a model (only the
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default manager is considered in these situations), Django will use that class
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@ -396,7 +401,8 @@ it, whereas the following will not work::
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# BAD: Incorrect code
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class MyManager(models.Manager):
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...
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# ...
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pass
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# Sets the attribute on an instance of MyManager. Django will
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# ignore this setting.
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@ -404,7 +410,7 @@ it, whereas the following will not work::
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mgr.use_for_related_fields = True
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class MyModel(models.Model):
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...
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# ...
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objects = mgr
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# End of incorrect code.
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@ -90,6 +90,8 @@ attributes. Be careful not to choose field names that conflict with the
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Example::
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from django.db import models
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class Musician(models.Model):
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first_name = models.CharField(max_length=50)
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last_name = models.CharField(max_length=50)
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@ -290,8 +292,11 @@ For example, if a ``Car`` model has a ``Manufacturer`` -- that is, a
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``Manufacturer`` makes multiple cars but each ``Car`` only has one
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``Manufacturer`` -- use the following definitions::
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from django.db import models
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class Manufacturer(models.Model):
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# ...
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pass
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class Car(models.Model):
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manufacturer = models.ForeignKey(Manufacturer)
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@ -340,8 +345,11 @@ For example, if a ``Pizza`` has multiple ``Topping`` objects -- that is, a
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``Topping`` can be on multiple pizzas and each ``Pizza`` has multiple toppings
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-- here's how you'd represent that::
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from django.db import models
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class Topping(models.Model):
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# ...
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pass
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class Pizza(models.Model):
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# ...
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@ -403,6 +411,8 @@ intermediate model. The intermediate model is associated with the
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that will act as an intermediary. For our musician example, the code would look
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something like this::
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from django.db import models
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class Person(models.Model):
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name = models.CharField(max_length=128)
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@ -583,6 +593,7 @@ It's perfectly OK to relate a model to one from another app. To do this, import
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the related model at the top of the file where your model is defined. Then,
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just refer to the other model class wherever needed. For example::
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from django.db import models
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from geography.models import ZipCode
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class Restaurant(models.Model):
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@ -630,6 +641,8 @@ Meta options
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Give your model metadata by using an inner ``class Meta``, like so::
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from django.db import models
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class Ox(models.Model):
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horn_length = models.IntegerField()
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@ -660,6 +673,8 @@ model.
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For example, this model has a few custom methods::
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from django.db import models
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class Person(models.Model):
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first_name = models.CharField(max_length=50)
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last_name = models.CharField(max_length=50)
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@ -729,6 +744,8 @@ A classic use-case for overriding the built-in methods is if you want something
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to happen whenever you save an object. For example (see
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:meth:`~Model.save` for documentation of the parameters it accepts)::
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from django.db import models
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class Blog(models.Model):
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name = models.CharField(max_length=100)
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tagline = models.TextField()
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@ -740,6 +757,8 @@ to happen whenever you save an object. For example (see
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You can also prevent saving::
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from django.db import models
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class Blog(models.Model):
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name = models.CharField(max_length=100)
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tagline = models.TextField()
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@ -826,6 +845,8 @@ the child (and Django will raise an exception).
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An example::
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from django.db import models
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class CommonInfo(models.Model):
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name = models.CharField(max_length=100)
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age = models.PositiveIntegerField()
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@ -854,14 +875,16 @@ attribute. If a child class does not declare its own :ref:`Meta <meta-options>`
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class, it will inherit the parent's :ref:`Meta <meta-options>`. If the child wants to
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extend the parent's :ref:`Meta <meta-options>` class, it can subclass it. For example::
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from django.db import models
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class CommonInfo(models.Model):
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...
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# ...
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class Meta:
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abstract = True
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ordering = ['name']
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class Student(CommonInfo):
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...
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# ...
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class Meta(CommonInfo.Meta):
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db_table = 'student_info'
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@ -901,6 +924,8 @@ abstract base class (only), part of the name should contain
|
|||
|
||||
For example, given an app ``common/models.py``::
|
||||
|
||||
from django.db import models
|
||||
|
||||
class Base(models.Model):
|
||||
m2m = models.ManyToManyField(OtherModel, related_name="%(app_label)s_%(class)s_related")
|
||||
|
||||
|
@ -949,6 +974,8 @@ relationship introduces links between the child model and each of its parents
|
|||
(via an automatically-created :class:`~django.db.models.OneToOneField`).
|
||||
For example::
|
||||
|
||||
from django.db import models
|
||||
|
||||
class Place(models.Model):
|
||||
name = models.CharField(max_length=50)
|
||||
address = models.CharField(max_length=80)
|
||||
|
@ -998,7 +1025,7 @@ If the parent has an ordering and you don't want the child to have any natural
|
|||
ordering, you can explicitly disable it::
|
||||
|
||||
class ChildModel(ParentModel):
|
||||
...
|
||||
# ...
|
||||
class Meta:
|
||||
# Remove parent's ordering effect
|
||||
ordering = []
|
||||
|
@ -1061,15 +1088,21 @@ Proxy models are declared like normal models. You tell Django that it's a
|
|||
proxy model by setting the :attr:`~django.db.models.Options.proxy` attribute of
|
||||
the ``Meta`` class to ``True``.
|
||||
|
||||
For example, suppose you want to add a method to the ``Person`` model described
|
||||
above. You can do it like this::
|
||||
For example, suppose you want to add a method to the ``Person`` model. You can do it like this::
|
||||
|
||||
from django.db import models
|
||||
|
||||
class Person(models.Model):
|
||||
first_name = models.CharField(max_length=30)
|
||||
last_name = models.CharField(max_length=30)
|
||||
|
||||
class MyPerson(Person):
|
||||
class Meta:
|
||||
proxy = True
|
||||
|
||||
def do_something(self):
|
||||
...
|
||||
# ...
|
||||
pass
|
||||
|
||||
The ``MyPerson`` class operates on the same database table as its parent
|
||||
``Person`` class. In particular, any new instances of ``Person`` will also be
|
||||
|
@ -1125,8 +1158,11 @@ classes will still be available.
|
|||
Continuing our example from above, you could change the default manager used
|
||||
when you query the ``Person`` model like this::
|
||||
|
||||
from django.db import models
|
||||
|
||||
class NewManager(models.Manager):
|
||||
...
|
||||
# ...
|
||||
pass
|
||||
|
||||
class MyPerson(Person):
|
||||
objects = NewManager()
|
||||
|
|
|
@ -17,6 +17,8 @@ models, which comprise a Weblog application:
|
|||
|
||||
.. code-block:: python
|
||||
|
||||
from django.db import models
|
||||
|
||||
class Blog(models.Model):
|
||||
name = models.CharField(max_length=100)
|
||||
tagline = models.TextField()
|
||||
|
|
Loading…
Reference in New Issue