      toppings = models.ManyToManyField('Topping', related_name='pizzas')
  
  
  class Album(models.Model):
      owner = models.ForeignKey(User, null=True, blank=True, on_delete=models.SET_NULL)
      title = models.CharField(max_length=30)
  
  
  class Employee(Person):
      code = models.CharField(max_length=20)
 
</s> remove     owner = models.ForeignKey(User)
 </s> add     owner = models.ForeignKey(User, models.CASCADE) </s> remove     owner = models.ForeignKey(Collector)
 </s> add     owner = models.ForeignKey(Collector, models.CASCADE) </s> remove     owner = models.ForeignKey(Collector)
 </s> add     owner = models.ForeignKey(Collector, models.CASCADE) </s> remove     owner = models.ForeignKey(Collector)
 </s> add     owner = models.ForeignKey(Collector, models.CASCADE) </s> remove     parent = models.ForeignKey('self', null=True, on_delete=models.SET_NULL)
    soulmate = models.ForeignKey('self', null=True, on_delete=models.CASCADE, related_name='soulmates')
 </s> add     parent = models.ForeignKey('self', models.SET_NULL, null=True)
    soulmate = models.ForeignKey('self', models.CASCADE, null=True, related_name='soulmates')
    owner = models.ForeignKey(User, models.SET_NULL, null=True, blank=True)
      toppings = models.ManyToManyField('Topping', related_name='pizzas')
  
  
  class Album(models.Model):
    owner = models.ForeignKey(User, models.SET_NULL, null=True, blank=True)
      title = models.CharField(max_length=30)
  
  
  class Employee(Person):
      code = models.CharField(max_length=20)
keep keep keep keep replace keep keep keep keep keep
 Fixed #21127 -- Started deprecation toward requiring on_delete for ForeignKey/OneToOneField 
tests/admin_views/models.py