Thanks for the answers. Still not sure why it would not implement ON
DELETE CASCADE in the DB itself. But whatever.
Regards,
Dennis
On 20/01/2023 20:15, Jason wrote:
https://docs.djangoproject.com/en/4.1/ref/models/fields/#django.db.models.CASCADE
> Django emulates the behavior of the SQL constraint ON DELETE CASCADE
and also deletes the object containing the ForeignKey.
this is specified in the docs.
https://code.djangoproject.com/ticket/21961
On Friday, January 20, 2023 at 10:44:48 AM UTC-5 bhuvn...@gmail.com wrote:
Hi dennis,
You can open a ticket on the trac
(https://code.djangoproject.com/query) for whatever issue you are
facing.It will be easier to understand there.
Regards
Bhuvnesh
On Fri, Jan 20, 2023, 8:36 PM Dennis Tants <ta...@uni-bremen.de>
wrote:
Hey folks,
I recently came across what I think is a bug. Let me try to
explain it as detailed as possible.
Imagine I have two models, one is called Events, the other is
called EventAccounts. EventAccounts can't exist without an
Event, so I added a ForeignKey with the
on_delete=models.CASCADE constraint to one field of
EventAccounts. Should I delete an event, the corresponding
event accounts will also be deleted. This works just fine when
using Django itself (or the admin pages). See my models.py.
models.py:
class Events(models.Model):
...
class EventAccounts(models.Model):
...
account_event = models.ForeignKey(Events,
on_delete=models.CASCADE)
...
Now one of my tasks is to cleanup the database every day to
delete events, which ended more than two weeks ago. I was
thinking of creating a cronjob to run raw SQL every day. When
running this command:
DELETE FROM app_eventtool_events WHERE event_end_date <
(NOW() - INTERVAL 14 DAY);
I always get informed that there is an existing child and the
events do not get deleted. Which is why I had a look at the
table constraints with:
SHOW CREATE TABLE app_eventtool_eventaccounts;
It seems that the ON DELETE CASCADE statement at the end is
missing:
CONSTRAINT
`app_eventtool_eventa_account_event_id_0ff3718a_fk_app_event`
FOREIGN KEY (`account_event_id`) REFERENCES
`app_eventtool_events` (`event_id`)
If I now delete the above constraint and add a selfmade one,
it looks like this:
ALTER TABLE app_eventtool_eventaccounts ADD CONSTRAINT
app_eventtool_events_account_event_id FOREIGN KEY
(account_event_id) REFERENCES app_eventtool_events (event_id)
ON DELETE CASCADE ON UPDATE NO ACTION;
CONSTRAINT `app_eventtool_events_account_event_id` FOREIGN
KEY (`account_event_id`) REFERENCES `app_eventtool_events`
(`event_id`) ON DELETE CASCADE ON UPDATE NO ACTION
As you can see, ON DELETE CASCADE is now present. Now I am
also able to delete the events with raw SQL as mentioned
above. This is reproducible when dropping and creating the
database fully. Updating from version 4.0.6 to version 4.1.5
did not solve the problem.
Furthermore I started testing a bit with the on_delete
statement in models.py. I changed models.CASCADE to
models.RESTRICT and created a new migration. The migration
file itself looks fine. But when trying to get the raw SQL of
the migration via:
python3 manage.py sqlmigrate app_eventtool 0002
it basically results in an empty migration:
--
-- Alter field account_event on eventaccounts
--
-- (no-op)
Maybe this is expected behaviour, but for me it seems like a
bug. Can anyone confirm/deny this?
Thanks in advance,
Dennis
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