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