185 lines
4.0 KiB
Python
185 lines
4.0 KiB
Python
"""
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XX. Model inheritance
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Model inheritance exists in two varieties:
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- abstract base classes which are a way of specifying common
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information inherited by the subclasses. They don't exist as a separate
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model.
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- non-abstract base classes (the default), which are models in their own
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right with their own database tables and everything. Their subclasses
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have references back to them, created automatically.
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Both styles are demonstrated here.
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"""
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from django.db import models
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#
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# Abstract base classes
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#
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class CommonInfo(models.Model):
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name = models.CharField(max_length=50)
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age = models.PositiveIntegerField()
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class Meta:
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abstract = True
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ordering = ["name"]
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def __str__(self):
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return "%s %s" % (self.__class__.__name__, self.name)
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class Worker(CommonInfo):
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job = models.CharField(max_length=50)
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class Student(CommonInfo):
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school_class = models.CharField(max_length=10)
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class Meta:
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pass
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#
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# Abstract base classes with related models
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#
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class Post(models.Model):
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title = models.CharField(max_length=50)
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class Attachment(models.Model):
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post = models.ForeignKey(
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Post,
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models.CASCADE,
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related_name="attached_%(class)s_set",
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related_query_name="attached_%(app_label)s_%(class)ss",
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)
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content = models.TextField()
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class Meta:
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abstract = True
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class Comment(Attachment):
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is_spam = models.BooleanField(default=False)
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class Link(Attachment):
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url = models.URLField()
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#
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# Multi-table inheritance
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#
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class Chef(models.Model):
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name = models.CharField(max_length=50)
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class Place(models.Model):
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name = models.CharField(max_length=50)
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address = models.CharField(max_length=80)
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class Rating(models.Model):
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rating = models.IntegerField(null=True, blank=True)
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class Meta:
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abstract = True
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ordering = ["-rating"]
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class Restaurant(Place, Rating):
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serves_hot_dogs = models.BooleanField(default=False)
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serves_pizza = models.BooleanField(default=False)
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chef = models.ForeignKey(Chef, models.SET_NULL, null=True, blank=True)
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class Meta(Rating.Meta):
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db_table = "my_restaurant"
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class ItalianRestaurant(Restaurant):
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serves_gnocchi = models.BooleanField(default=False)
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class Supplier(Place):
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customers = models.ManyToManyField(Restaurant, related_name="provider")
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class ParkingLot(Place):
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# An explicit link to the parent (we can control the attribute name).
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parent = models.OneToOneField(
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Place, models.CASCADE, primary_key=True, parent_link=True
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)
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main_site = models.ForeignKey(Place, models.CASCADE, related_name="lot")
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#
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# Abstract base classes with related models where the sub-class has the
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# same name in a different app and inherits from the same abstract base
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# class.
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# NOTE: The actual API tests for the following classes are in
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# model_inheritance_same_model_name/models.py - They are defined
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# here in order to have the name conflict between apps
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#
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class Title(models.Model):
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title = models.CharField(max_length=50)
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class NamedURL(models.Model):
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title = models.ForeignKey(
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Title, models.CASCADE, related_name="attached_%(app_label)s_%(class)s_set"
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)
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url = models.URLField()
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class Meta:
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abstract = True
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class Mixin:
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def __init__(self):
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self.other_attr = 1
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super().__init__()
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class MixinModel(models.Model, Mixin):
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pass
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class Base(models.Model):
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titles = models.ManyToManyField(Title)
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class SubBase(Base):
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sub_id = models.IntegerField(primary_key=True)
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class GrandParent(models.Model):
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first_name = models.CharField(max_length=80)
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last_name = models.CharField(max_length=80)
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email = models.EmailField(unique=True)
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place = models.ForeignKey(Place, models.CASCADE, null=True, related_name="+")
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class Meta:
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# Ordering used by test_inherited_ordering_pk_desc.
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ordering = ["-pk"]
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unique_together = ("first_name", "last_name")
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class Parent(GrandParent):
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pass
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class Child(Parent):
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pass
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class GrandChild(Child):
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pass
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