What does on_delete do on Django models?
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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 asPROTECT
that matches SQL’sRESTRICT
more accurately.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