          # Disable reverse relation
          kwargs['related_name'] = '+'
          # Set unique to enable model cache.
          kwargs['unique'] = True
          super(CurrentTranslation, self).__init__(to, from_fields, to_fields, **kwargs)
  
  
  class ArticleTranslation(models.Model):
  
      article = models.ForeignKey('indexes.Article')
 
</s> remove     def __init__(self, to, from_fields, to_fields, **kwargs):
 </s> add     def __init__(self, to, on_delete, from_fields, to_fields, **kwargs): </s> remove     article = models.ForeignKey('indexes.Article')
 </s> add     article = models.ForeignKey('indexes.Article', models.CASCADE) </s> remove     reporter = models.ForeignKey(ProxyTrackerUser)
    associated_bug = models.ForeignKey(ProxyProxyBug)
 </s> add     reporter = models.ForeignKey(ProxyTrackerUser, models.CASCADE)
    associated_bug = models.ForeignKey(ProxyProxyBug, models.CASCADE) </s> remove     translation = CurrentTranslation(ArticleTranslation, ['id'], ['article'])
 </s> add     translation = CurrentTranslation(ArticleTranslation, models.CASCADE, ['id'], ['article'])
        super(CurrentTranslation, self).__init__(to, on_delete, from_fields, to_fields, **kwargs)
          # Disable reverse relation
          kwargs['related_name'] = '+'
          # Set unique to enable model cache.
          kwargs['unique'] = True
        super(CurrentTranslation, self).__init__(to, on_delete, from_fields, to_fields, **kwargs)
  
  
  class ArticleTranslation(models.Model):
  
      article = models.ForeignKey('indexes.Article')
keep keep keep keep replace keep keep keep keep keep
 Fixed #21127 -- Started deprecation toward requiring on_delete for ForeignKey/OneToOneField 
tests/indexes/models.py