#27406: Signals pre_delete and post_delete break logical relationship of models
and
behave in diffrently with different backends
-------------------------------------+-------------------------------------
Reporter: Seti | Owner: nobody
Type: Uncategorized | Status: new
Component: Database layer | Version: 1.10
(models, ORM) |
Severity: Normal | Resolution:
Keywords: Databases | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Seti):
Replying to [comment:3 Tim Graham]:
> Resolved.
If a field has attributes null=True and blank=True, and using signals
pre_delete (as example) attribute "on_delete" does not working at all.
I tried on_delete=models.CASCADE and models.SET_NULL, it is does not
working.
I made dived deep in SQL generate from the Django ORM.
On my code (with activate signal "pre_delete")
{{{
User.objects.filter().delete()
}}}
it generated a next code (a main part):
{{{
DELETE FROM "users_user" WHERE "users_user"."id" IN ('87420c3a-
dae9-4c87-9095-064d8806530b'::uuid)
DELETE FROM "users_profile" WHERE "users_profile"."id" IN
('f4d4aa39-e645-4da0-aef3-c2853c5d5e91'::uuid)
DELETE FROM "diaries_diary" WHERE "diaries_diary"."id" IN
('b12f5507-3957-4384-ab32-9ffbf30acd87'::uuid)
INSERT INTO "notifications_notification" ("id", "level", "action",
"is_read", "is_deleted", "is_public", "is_emailed", "created",
"is_anonimuos", "user_id", "user_display_text", "target_content_type_id",
"target_object_id", "target_display_text",
"action_target_content_type_id", "action_target_object_id") VALUES
('1d2b02d2-aec0-45fd-a23f-ef01262f4960'::uuid, 'success', 'deleted_user',
false, false, true, true, '2016-11-08T09:38:08.317519+00:00'::timestamptz,
false, '87420c3a-dae9-4c87-9095-064d8806530b'::uuid, 'uкузнецов
([email protected])', NULL, NULL, NULL, NULL, NULL)
UPDATE "notifications_notification" SET "level" = 'success', "action" =
'deleted_user', "is_read" = false, "is_deleted" = false, "is_public" =
true, "is_emailed" = true, "created" = NULL, "is_anonimuos" = false,
"user_id" = '87420c3a-dae9-4c87-9095-064d8806530b'::uuid,
"user_display_text" = 'uкузнецов ([email protected])'',
"target_content_type_id" = NULL, "target_object_id" = NULL,
"target_display_text" = NULL, "action_target_content_type_id" = NULL,
"action_target_object_id" = NULL WHERE "notifications_notification"."id" =
'1d2b02d2-aec0-45fd-a23f-ef01262f4960'::uuid
}}}
An error is here
{{{
"user_id" = '87420c3a-dae9-4c87-9095-064d8806530b'::uuid,
"user_display_text" = 'uкузнецов ([email protected])''
}}}
**"user_id" must be NULL**, because a user must be deleted
On a python side it is resolved very simple
{{{
class Notification(models.Model):
..........................
def save(self, *args, **kwargs):
..................................
user = kwargs.pop('user', None)
if user is not None:
# user will be deleted, so we keep it full name for display
self.user_display_text = user.get_full_name()
# manualy set field "user" to None (NULL in SQL), because the
Django does not made it
self.user = None
self.full_clean()
super(Notification, self).save(*args, **kwargs)
}}}
So, dear the Django developer team, please point this caution about using
signals "pre_delete" and "post_delete" in the docs.
--
Ticket URL: <https://code.djangoproject.com/ticket/27406#comment:4>
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