      pages = models.IntegerField()
      rating = models.FloatField()
      price = models.DecimalField(decimal_places=2, max_digits=6)
      authors = models.ManyToManyField(Author)
      contact = models.ForeignKey(Author, related_name='book_contact_set')
      publisher = models.ForeignKey(Publisher)
      pubdate = models.DateField()
  
      def __str__(self):
          return self.name
  
 
</s> remove     contact = models.ForeignKey(Author, related_name='book_contact_set')
    publisher = models.ForeignKey(Publisher)
 </s> add     contact = models.ForeignKey(Author, models.CASCADE, related_name='book_contact_set')
    publisher = models.ForeignKey(Publisher, models.CASCADE) </s> remove     contact = models.ForeignKey(Author, related_name='book_contact_set')
    publisher = models.ForeignKey(Publisher)
 </s> add     contact = models.ForeignKey(Author, models.CASCADE, related_name='book_contact_set')
    publisher = models.ForeignKey(Publisher, models.CASCADE) </s> remove     team_leader = models.ForeignKey(Villain, related_name='lead_plots')
    contact = models.ForeignKey(Villain, related_name='contact_plots')
 </s> add     team_leader = models.ForeignKey(Villain, models.CASCADE, related_name='lead_plots')
    contact = models.ForeignKey(Villain, models.CASCADE, related_name='contact_plots') </s> remove     author = models.ForeignKey(Author, related_name='fans')
 </s> add     author = models.ForeignKey(Author, models.CASCADE, related_name='fans') </s> remove     publisher = models.ForeignKey(Publisher, related_name='books', db_column="publisher_id_column")
 </s> add     publisher = models.ForeignKey(
        Publisher,
        models.CASCADE,
        related_name='books',
        db_column="publisher_id_column",
    )
    contact = models.ForeignKey(Author, models.CASCADE, related_name='book_contact_set')
    publisher = models.ForeignKey(Publisher, models.CASCADE)
      pages = models.IntegerField()
      rating = models.FloatField()
      price = models.DecimalField(decimal_places=2, max_digits=6)
      authors = models.ManyToManyField(Author)
    contact = models.ForeignKey(Author, models.CASCADE, related_name='book_contact_set')
    publisher = models.ForeignKey(Publisher, models.CASCADE)
    contact = models.ForeignKey(Author, models.CASCADE, related_name='book_contact_set')
    publisher = models.ForeignKey(Publisher, models.CASCADE)
      pubdate = models.DateField()
  
      def __str__(self):
          return self.name
  
keep keep keep keep replace replace keep keep keep keep keep
 Fixed #21127 -- Started deprecation toward requiring on_delete for ForeignKey/OneToOneField 
tests/aggregation/models.py