      serial = models.IntegerField()
  
  
  class UserSite(models.Model):
      user = models.ForeignKey(User, to_field="username")
      data = models.IntegerField()
  
  
  class UserProfile(models.Model):
      user = models.ForeignKey(User, unique=True, to_field="username")
 
</s> remove     user = models.ForeignKey(User, unique=True, to_field="username")
 </s> add     user = models.ForeignKey(User, models.CASCADE, unique=True, to_field="username") </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     user = models.OneToOneField(User, primary_key=True)
 </s> add     user = models.OneToOneField(User, models.CASCADE, primary_key=True) </s> remove     user = models.ForeignKey('auth.User', 'username')
 </s> add     user = models.ForeignKey('auth.User', models.CASCADE, to_field='username') </s> remove     holder = models.ForeignKey(Holder2)
 </s> add     holder = models.ForeignKey(Holder2, models.CASCADE)
    user = models.ForeignKey(User, models.CASCADE, to_field="username")
      serial = models.IntegerField()
  
  
  class UserSite(models.Model):
    user = models.ForeignKey(User, models.CASCADE, to_field="username")
      data = models.IntegerField()
  
  
  class UserProfile(models.Model):
      user = models.ForeignKey(User, unique=True, to_field="username")
keep keep keep keep replace keep keep keep keep keep
 Fixed #21127 -- Started deprecation toward requiring on_delete for ForeignKey/OneToOneField 
tests/model_formsets_regress/models.py