Cross-instance issues for ConditionalVersionField

[kevinmsun]

I'm using ConditionalVersionField for a model, specifically with ignore_fields configured in my ConcurrencyMeta. I'm finding that, when multiple instances of the class are loaded simultaneously, the initial is being shared/overwritten rather than being uniquely maintained per instance, thus leading to significantly more version bumps (and RecordModifiedErrors) than expected

In my observations, the models are loaded and the initial is recorded in _concurrencymeta at

django-concurrency/src/concurrency/fields.py

Line 335 in b915a3c

instance._concurrencymeta.initial = self._get_hash(instance)

. However, the ._concurrencymeta actually appears to be shared across all my instances, meaning that each loaded instance overwrites the recorded initial value for preceding instances. When it's consulted to check for changes (

django-concurrency/src/concurrency/fields.py

Lines 370 to 373 in b915a3c

	old = model_instance._concurrencymeta.initial
	new = self._get_hash(model_instance)
	if old != new:
	return int(getattr(model_instance, self.attname, 0) + 1)

), it "always" returns an incremented value (unless I happen to be operating on the last instance loaded).

[saxix]

@kevinmsun I see the point, and it seems this is a bug. You are right when you say that _concurrencymeta is shared because it is a class attribute

We need to change the line you pointed out as

instance._concurrencymeta_initial = self._get_hash(instance) 

and change the three places where it is used.

I do not have the time to work on this right now, but I'll be happy to get a PR if you want.

[kevinmsun]

@saxix thanks for the information/review.

What's the recommended process to contribute? I tried pushing a branch in order to open a PR, but was denied access; do you recommend forking or something like that?

[saxix]

@kevinmsun, you can fork the repo and make a pr from your repo in github. You can use the same process as described here https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/working-with-git/