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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 __future__ import unicode_literals
from django.db import models
from django.utils.encoding import python_2_unicode_compatible
#
# Abstract base classes
#
@python_2_unicode_compatible
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)
@python_2_unicode_compatible
class Attachment(models.Model):
post = models.ForeignKey(Post, models.CASCADE, related_name='attached_%(class)s_set')
content = models.TextField()
class Meta:
abstract = True
def __str__(self):
return self.content
class Comment(Attachment):
is_spam = models.BooleanField(default=False)
class Link(Attachment):
url = models.URLField()
#
# Multi-table inheritance
#
@python_2_unicode_compatible
class Chef(models.Model):
name = models.CharField(max_length=50)
def __str__(self):
return "%s the chef" % self.name
@python_2_unicode_compatible
class Place(models.Model):
name = models.CharField(max_length=50)
address = models.CharField(max_length=80)
def __str__(self):
return "%s the place" % self.name
class Rating(models.Model):
rating = models.IntegerField(null=True, blank=True)
class Meta:
abstract = True
ordering = ['-rating']
@python_2_unicode_compatible
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'
def __str__(self):
return "%s the restaurant" % self.name
@python_2_unicode_compatible
class ItalianRestaurant(Restaurant):
serves_gnocchi = models.BooleanField(default=False)
def __str__(self):
return "%s the italian restaurant" % self.name
@python_2_unicode_compatible
class Supplier(Place):
customers = models.ManyToManyField(Restaurant, related_name='provider')
def __str__(self):
return "%s the supplier" % self.name
@python_2_unicode_compatible
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')
def __str__(self):
return "%s the parking lot" % self.name
#
# 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
@python_2_unicode_compatible
class Copy(NamedURL):
content = models.TextField()
def __str__(self):
return self.content
class Mixin(object):
def __init__(self):
self.other_attr = 1
super(Mixin, self).__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)
class Meta:
unique_together = ('first_name', 'last_name')
class Parent(GrandParent):
pass
class Child(Parent):
pass
class GrandChild(Child):
pass
|
