          AuthorWithAge, related_name='books_with_year')
  
  
  class Bio(models.Model):
      author = models.OneToOneField(Author)
      books = models.ManyToManyField(Book, blank=True)
  
  
  @python_2_unicode_compatible
  class Reader(models.Model):
 
</s> remove     book = models.OneToOneField(Book, parent_link=True)
 </s> add     book = models.OneToOneField(Book, models.CASCADE, parent_link=True) </s> remove         author = models.ForeignKey(Author)
 </s> add         author = models.ForeignKey(Author, on_delete=models.CASCADE) </s> remove     author = models.ForeignKey(Author, to_field='name', related_name='addresses')
 </s> add     author = models.ForeignKey(Author, models.CASCADE, to_field='name', related_name='addresses') </s> remove     chef = models.ForeignKey(Chef, null=True, blank=True)
 </s> add     chef = models.ForeignKey(Chef, models.SET_NULL, null=True, blank=True) </s> remove     author = models.OneToOneField(Author, parent_link=True)
 </s> add     author = models.OneToOneField(Author, models.CASCADE, parent_link=True)
    author = models.OneToOneField(Author, models.CASCADE)
          AuthorWithAge, related_name='books_with_year')
  
  
  class Bio(models.Model):
    author = models.OneToOneField(Author, models.CASCADE)
      books = models.ManyToManyField(Book, blank=True)
  
  
  @python_2_unicode_compatible
  class Reader(models.Model):
keep keep keep keep replace keep keep keep keep keep
 Fixed #21127 -- Started deprecation toward requiring on_delete for ForeignKey/OneToOneField 
tests/prefetch_related/models.py