How to deal on a `self.model.MultipleObjectsReturned` exception on `CrontabSchedule`?

[joachimesque]

Hi!
I’m running django-celery-beat 2.6.0 (the app is a Bookwyrm instance)

Following a server move for my app, I discovered that I have regular self.model.MultipleObjectsReturned exceptions when trying to access my CrontabSchedule

>>> CrontabSchedule.objects.all()
<QuerySet [<CrontabSchedule: 0 4 * * * (m/h/dM/MY/d) UTC>, <CrontabSchedule: 0 4 * * * (m/h/dM/MY/d) UTC>]>
>>> CrontabSchedule.objects.first().periodictask_set.all()
<PeriodicTaskQuerySet [<PeriodicTask: celery.backend_cleanup: 0 4 * * * (m/h/dM/MY/d) UTC>, <PeriodicTask: celery.backend_cleanup: 0 4 * * * (m/h/dM/MY/d) UTC>]>
>>> CrontabSchedule.objects.last().periodictask_set.all()
<PeriodicTaskQuerySet [<PeriodicTask: celery.backend_cleanup: 0 4 * * * (m/h/dM/MY/d) UTC>, <PeriodicTask: celery.backend_cleanup: 0 4 * * * (m/h/dM/MY/d) UTC>]>

If I try to delete it:

>>> CrontabSchedule.objects.last().delete()
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/usr/local/lib/python3.11/site-packages/django/db/models/base.py", line 1132, in delete
    return collector.delete()
           ^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/models/deletion.py", line 463, in delete
    signals.pre_delete.send(
  File "/usr/local/lib/python3.11/site-packages/django/dispatch/dispatcher.py", line 176, in send
    return [
           ^
  File "/usr/local/lib/python3.11/site-packages/django/dispatch/dispatcher.py", line 177, in <listcomp>
    (receiver, receiver(signal=self, sender=sender, **named))
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django_celery_beat/models.py", line 394, in changed
    cls.update_changed()
  File "/usr/local/lib/python3.11/site-packages/django_celery_beat/models.py", line 398, in update_changed
    cls.objects.update_or_create(ident=1, defaults={'last_update': now()})
  File "/usr/local/lib/python3.11/site-packages/django/db/models/manager.py", line 87, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/models/query.py", line 949, in update_or_create
    obj, created = self.select_for_update().get_or_create(defaults, **kwargs)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/models/query.py", line 916, in get_or_create
    return self.get(**kwargs), False
           ^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/models/query.py", line 640, in get
    raise self.model.MultipleObjectsReturned(
django_celery_beat.models.PeriodicTasks.MultipleObjectsReturned: get() returned more than one PeriodicTasks -- it returned 2!

The same error is returned when I run >>> CrontabSchedule.objects.last().periodictask_set.last().delete().

>>> from django_celery_beat.models import PeriodicTask
>>> PeriodicTask.objects.all()
Traceback (most recent call last):
  File "/usr/local/lib/python3.11/site-packages/django/db/models/fields/related_descriptors.py", line 218, in __get__
    rel_obj = self.field.get_cached_value(instance)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/models/fields/mixins.py", line 15, in get_cached_value
    return instance._state.fields_cache[cache_name]
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^
KeyError: 'crontab'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/usr/local/lib/python3.11/site-packages/django/db/models/query.py", line 377, in __repr__
    return "<%s %r>" % (self.__class__.__name__, data)
                                                 ^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/models/base.py", line 588, in __repr__
    return "<%s: %s>" % (self.__class__.__name__, self)
                                                  ^^^^
  File "/usr/local/lib/python3.11/site-packages/django_celery_beat/models.py", line 625, in __str__
    if self.crontab:
       ^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/models/fields/related_descriptors.py", line 236, in __get__
    rel_obj = self.get_object(instance)
              ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/models/fields/related_descriptors.py", line 199, in get_object
    return qs.get(self.field.get_reverse_related_filter(instance))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/models/query.py", line 640, in get
    raise self.model.MultipleObjectsReturned(
django_celery_beat.models.CrontabSchedule.MultipleObjectsReturned: get() returned more than one CrontabSchedule -- it returned 2!

>>> PeriodicTask.objects.last()
<PeriodicTask: check-for-updates: chaque jour>

>>> PeriodicTask.objects.first()
Traceback (most recent call last):
  File "/usr/local/lib/python3.11/site-packages/django/db/models/fields/related_descriptors.py", line 218, in __get__
    rel_obj = self.field.get_cached_value(instance)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/models/fields/mixins.py", line 15, in get_cached_value
    return instance._state.fields_cache[cache_name]
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^
KeyError: 'crontab'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/usr/local/lib/python3.11/site-packages/django/db/models/base.py", line 588, in __repr__
    return "<%s: %s>" % (self.__class__.__name__, self)
                                                  ^^^^
  File "/usr/local/lib/python3.11/site-packages/django_celery_beat/models.py", line 625, in __str__
    if self.crontab:
       ^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/models/fields/related_descriptors.py", line 236, in __get__
    rel_obj = self.get_object(instance)
              ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/models/fields/related_descriptors.py", line 199, in get_object
    return qs.get(self.field.get_reverse_related_filter(instance))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/models/query.py", line 640, in get
    raise self.model.MultipleObjectsReturned(
django_celery_beat.models.CrontabSchedule.MultipleObjectsReturned: get() returned more than one CrontabSchedule -- it returned 2!

How serious do you think this error is?
How would I go fixing it?

Thanks!

[auvipy]

it seems you are getting a return instance._state.fields_cache[cache_name]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^
KeyError: 'crontab' error. may be it is your code not the project? let me know what you get

[cclauss]

django-celery-beat 2.6.0

Do you get the same error if you upgrade to the current version of django-celery-beat?