      tag = models.SlugField()
      content_type = models.ForeignKey(ContentType, related_name="taggeditem_set2")
      object_id = models.PositiveIntegerField()
      content_object = GenericForeignKey('content_type', 'object_id')
      created_by_ct = models.ForeignKey(ContentType, null=True,
                                        related_name='taggeditem_set3')
      created_by_fkey = models.PositiveIntegerField(null=True)
      created_by = GenericForeignKey('created_by_ct', 'created_by_fkey',)
      favorite_ct = models.ForeignKey(ContentType, null=True,
                                      related_name='taggeditem_set4')
      favorite_fkey = models.CharField(max_length=64, null=True)
 
</s> remove     favorite_ct = models.ForeignKey(ContentType, null=True,
                                    related_name='taggeditem_set4')
 </s> add     favorite_ct = models.ForeignKey(
        ContentType,
        models.SET_NULL,
        null=True,
        related_name='taggeditem_set4',
    ) </s> remove     content_type = models.ForeignKey(ContentType, related_name="taggeditem_set2")
 </s> add     content_type = models.ForeignKey(
        ContentType,
        models.CASCADE,
        related_name="taggeditem_set2",
    ) </s> remove     content_type = models.ForeignKey(ContentType, related_name='tagged_items')
 </s> add     content_type = models.ForeignKey(ContentType, models.CASCADE, related_name='tagged_items') </s> remove     content_type = models.ForeignKey(ContentType)
 </s> add     content_type = models.ForeignKey(ContentType, models.CASCADE) </s> remove     content_type = models.ForeignKey(ContentType, related_name='backend_tags')
 </s> add     content_type = models.ForeignKey(ContentType, models.CASCADE, related_name='backend_tags')
    created_by_ct = models.ForeignKey(
        ContentType,
        models.SET_NULL,
        null=True,
        related_name='taggeditem_set3',
    )
      tag = models.SlugField()
      content_type = models.ForeignKey(ContentType, related_name="taggeditem_set2")
      object_id = models.PositiveIntegerField()
      content_object = GenericForeignKey('content_type', 'object_id')
    created_by_ct = models.ForeignKey(
        ContentType,
        models.SET_NULL,
        null=True,
        related_name='taggeditem_set3',
    )
    created_by_ct = models.ForeignKey(
        ContentType,
        models.SET_NULL,
        null=True,
        related_name='taggeditem_set3',
    )
      created_by_fkey = models.PositiveIntegerField(null=True)
      created_by = GenericForeignKey('created_by_ct', 'created_by_fkey',)
      favorite_ct = models.ForeignKey(ContentType, null=True,
                                      related_name='taggeditem_set4')
      favorite_fkey = models.CharField(max_length=64, null=True)
keep keep keep keep replace replace keep keep keep keep keep
 Fixed #21127 -- Started deprecation toward requiring on_delete for ForeignKey/OneToOneField 
tests/prefetch_related/models.py