      """
      title = models.CharField(max_length=100)
      content = models.TextField()
      date = models.DateTimeField()
      section = models.ForeignKey(Section, null=True, blank=True)
      sub_section = models.ForeignKey(Section, null=True, blank=True, on_delete=models.SET_NULL, related_name='+')
  
      def __str__(self):
          return self.title
  
      def model_year(self):
 
</s> remove     author = models.ForeignKey(Author)
 </s> add     author = models.ForeignKey(Author, models.CASCADE) </s> remove     owner = models.ForeignKey(User, null=True, blank=True, on_delete=models.SET_NULL)
 </s> add     owner = models.ForeignKey(User, models.SET_NULL, null=True, blank=True) </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     parent = models.ForeignKey('self', blank=True, null=True,
            related_name='children')
    category = models.ForeignKey(NamedCategory, null=True, default=None)
 </s> add     parent = models.ForeignKey(
        'self',
        models.SET_NULL,
        blank=True, null=True,
        related_name='children',
    )
    category = models.ForeignKey(NamedCategory, models.SET_NULL, null=True, default=None) </s> remove     site = models.ForeignKey(Site, related_name="admin_articles")
 </s> add     site = models.ForeignKey(Site, models.CASCADE, related_name="admin_articles")
    section = models.ForeignKey(Section, models.CASCADE, null=True, blank=True)
    sub_section = models.ForeignKey(Section, models.SET_NULL, null=True, blank=True, related_name='+')
      """
      title = models.CharField(max_length=100)
      content = models.TextField()
      date = models.DateTimeField()
    section = models.ForeignKey(Section, models.CASCADE, null=True, blank=True)
    sub_section = models.ForeignKey(Section, models.SET_NULL, null=True, blank=True, related_name='+')
    section = models.ForeignKey(Section, models.CASCADE, null=True, blank=True)
    sub_section = models.ForeignKey(Section, models.SET_NULL, null=True, blank=True, related_name='+')
  
      def __str__(self):
          return self.title
  
      def model_year(self):
keep keep keep keep replace replace keep keep keep keep keep
 Fixed #21127 -- Started deprecation toward requiring on_delete for ForeignKey/OneToOneField 
tests/admin_views/models.py