PYTHON

django on_delete options

#ONDELETE CASCADE
your_foreign_key_field = models.ForeignKey(Your_Reference_Model, on_delete=models.CASCADE)

#ONDELETE SET_NULL
your_foreign_key_field = models.ForeignKey(Your_Reference_Model, on_delete=models.SET_NULL)

django on-delete options

There are seven possible actions to take when such event occurs:

CASCADE: When the referenced object is deleted, also delete the objects that have references to it 
  (when you remove a blog post for instance, you might want to delete comments as well). 
  SQL equivalent: CASCADE.
      
PROTECT: Forbid the deletion of the referenced object. 
  To delete it you will have to delete all objects that reference it manually. 
  SQL equivalent: RESTRICT.
    
RESTRICT: (introduced in Django 3.1) Similar behavior as PROTECT that matches SQL's RESTRICT more accurately. (See django documentation example)
SET_NULL: Set the reference to NULL (requires the field to be nullable). 
  For instance, when you delete a User, you might want to keep the comments he posted on blog posts, 
  but say it was posted by an anonymous (or deleted) user. 
  SQL equivalent: SET NULL.
    
SET_DEFAULT: Set the default value. SQL equivalent: SET DEFAULT.
    
SET(...): Set a given value. This one is not part of the SQL standard and is entirely handled by Django.
  
DO_NOTHING: Probably a very bad idea since this would create integrity issues in your database 
  (referencing an object that actually doesn't exist). SQL equivalent: NO ACTION.

on_delete django options

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