  
  @python_2_unicode_compatible
  class Issue(models.Model):
      summary = models.CharField(max_length=255)
      assignee = models.ForeignKey(ProxyTrackerUser)
  
      def __str__(self):
          return ':'.join((self.__class__.__name__, self.summary,))
  
  
 
</s> remove     parent = models.ForeignKey(UUIDPKParent)
 </s> add     parent = models.ForeignKey(UUIDPKParent, models.CASCADE) </s> remove     poet = models.ForeignKey(Poet)
 </s> add     poet = models.ForeignKey(Poet, models.CASCADE) </s> remove     network = models.ForeignKey(Network)
 </s> add     network = models.ForeignKey(Network, models.CASCADE) </s> remove     two = models.ForeignKey('CyclicTwo')
 </s> add     two = models.ForeignKey('CyclicTwo', models.CASCADE) </s> remove     country = models.ForeignKey(Country)
 </s> add     country = models.ForeignKey(Country, models.CASCADE)
    assignee = models.ForeignKey(ProxyTrackerUser, models.CASCADE)
  
  @python_2_unicode_compatible
  class Issue(models.Model):
      summary = models.CharField(max_length=255)
    assignee = models.ForeignKey(ProxyTrackerUser, models.CASCADE)
  
      def __str__(self):
          return ':'.join((self.__class__.__name__, self.summary,))
  
  
keep keep keep keep replace keep keep keep keep keep
 Fixed #21127 -- Started deprecation toward requiring on_delete for ForeignKey/OneToOneField 
tests/proxy_models/models.py