Validate schedule objects on save for faster, more informative failures

[stevecj]

Summary:

When an instance of a schedule model (e.g. CrontabSchedule) has a field with an invalid value, no error is displayed, and the task is (silently) not added to the current schedule. If an exception occurred when trying to create the record, then the problem would be much easier to detect and then much easier to diagnose once detected.

• Celery Version: 5.2.1
• Celery-Beat Version: 2.2.1

Exact steps to reproduce the issue:

1. Create a CrontabSchedule instance with an invalid value in any of its crontab fields.
2. Create a PeriodicTask instance with the above CrontabSchedule instance as its .crontab value.
3. See that the task never runs.

[auvipy]

is this from the discussion you opened?

[stevecj]

It is related to that. Yes. I was able to solve the problem that I opened the discussion about, but I it was very complicated to track down the cause.

[auvipy]

ok, can you check this PR #478?

[lvelvee]

django-celery-beat/django_celery_beat/schedulers.py

Lines 243 to 250 in eb2af29

	def all_as_schedule(self):
	debug('DatabaseScheduler: Fetching database schedule')
	s = {}
	for model in self.Model.objects.enabled():
	try:
	s[model.name] = self.Entry(model, app=self.app)
	except ValueError:
	pass

[stevecj]

@lvelvee Thanks for pasting that code that I should have included in my original description of the problem.

@auvipy I might be wrong, but I don't see that PR #478 addresses this issue of mine — though I really like what you're doing there.

[auvipy]

ok if you are welcome to come with a proposed improvement with a failing test