django model.ForeignKey.on_delete

https://docs.djangoproject.com/en/4.2/ref/models/fields/#django.db.models.ForeignKey.on_delete

The possible values for on_delete are found in django.db.models:

• CASCADE¶

  Cascade deletes. Django emulates the behavior of the SQL constraint ON DELETE CASCADE and also deletes the object containing the ForeignKey.

  Model.delete() isn’t called on related models, but the pre_delete and post_delete signals are sent for all deleted objects.

• PROTECT¶

  Prevent deletion of the referenced object by raising ProtectedError, a subclass of django.db.IntegrityError.

• RESTRICT¶

  Prevent deletion of the referenced object by raising RestrictedError (a subclass of django.db.IntegrityError). Unlike PROTECT, deletion of the referenced object is allowed if it also references a different object that is being deleted in the same operation, but via a CASCADE relationship.