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"""
Many-to-many relationships
To define a many-to-many relationship, use ``ManyToManyField()``.
In this example, an ``Article`` can be published in multiple ``Publication``
objects, and a ``Publication`` has multiple ``Article`` objects.
"""
from django.db import models
class Publication(models.Model):
title = models.CharField(max_length=30)
class Meta:
ordering = ("title",)
def __str__(self):
return self.title
class Tag(models.Model):
id = models.BigAutoField(primary_key=True)
name = models.CharField(max_length=50)
def __str__(self):
return self.name
class NoDeletedArticleManager(models.Manager):
def get_queryset(self):
return super().get_queryset().exclude(headline="deleted")
class Article(models.Model):
headline = models.CharField(max_length=100)
# Assign a string as name to make sure the intermediary model is
# correctly created. Refs #20207
publications = models.ManyToManyField(Publication, name="publications")
tags = models.ManyToManyField(Tag, related_name="tags")
authors = models.ManyToManyField("User", through="UserArticle")
objects = NoDeletedArticleManager()
class Meta:
ordering = ("headline",)
def __str__(self):
return self.headline
class User(models.Model):
username = models.CharField(max_length=20, unique=True)
def __str__(self):
return self.username
class UserArticle(models.Model):
user = models.ForeignKey(User, models.CASCADE, to_field="username")
article = models.ForeignKey(Article, models.CASCADE)
# Models to test correct related_name inheritance
class AbstractArticle(models.Model):
class Meta:
abstract = True
publications = models.ManyToManyField(
Publication, name="publications", related_name="+"
)
class InheritedArticleA(AbstractArticle):
pass
class InheritedArticleB(AbstractArticle):
pass
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