title: In Django, how can I avoid cascade deletions when using a GenericRelation?
body: <p>According to the <a href="https://docs.djangoproject.com/en/1.11/ref/contrib/contenttypes/#s-reverse-generic-relations" rel="nofollow noreferrer">Django Docs</a>, if I add a <code>GenericRelation</code> to my model, then when an instance of that model is deleted, it will cascade-delete anything with a <code>GenericForeignKey</code> pointing to it.</p>
  
  <p>I need the querying benefits of having a <code>GenericRelation</code>, but I do NOT want it cascade-deleting stuff (I can't believe potentially-catestrophic behavior is what the django people selected as the default...).</p>
  
  <p>Both the <code>GenericRelation</code> class and the <code>GenericForeignKey</code> class do not accept an <code>on_delete</code> param for customizing the behavior.  Is there a way I can avoid the cascade deletion?  The docs suggest possibly using the <code>pre_delete</code> signal, but the docs for that are skimpy so it's unclear how that can help me...</p>