Django 2.1 support

[Spawning off #18]

There seems to be an odd bug in django-mptt (or in the way Hordak is using django-mptt) that is preventing the account tree updating correctly in Django >= 2.1. I’ve therefore only marked Django < 2.1 as supported.

Travis is is testing on Django 2.1, but with failures allowed. The problematic test is hordak.tests.models.test_core.AccountTestCase.test_full_code_changes_on_update. It seems that the accounts tree is not having it’s left/right values set correctly, and therefore the PG trigger which recalculates the Account’s full_code makes a mistake.

[p-baum]

I think I got it. Tests passing.

Whenever a new account is inserted, mptt adjusts the lft and rght values of (possibly many) other accounts as part of its duty to maintain a valid tree. This mass database update leaves the affected in memory account objects with outdated and invalid tree information. Should any of these objects be used to save new data, the invalid tree data is inadvertently saved along with it thus corrupting the tree. Maths is not my strong point so I would err on the side of caution and assume that whenever a new account is inserted, all in memory objects hold invalid data. Seeing as we don’t actually need this tree data, I think it would be optimal to never load it in the first place but I haven’t found a way to avoid this. What I have found is a way to prevent the saving of it. The save() method accepts a keyword argument ‘update_fields’ which allows you to provide a list of fields to update while ignoring the others:

    def save(self, *args, **kwargs):
        is_creating = not bool(self.pk)
        if is_creating:
            update_fields = None
        else:
            update_fields = [
                'uuid', 'name', 'parent', 'code', 'type',
                'is_bank_account', 'currencies'
            ]
        super(Account, self).save(*args, update_fields=update_fields, **kwargs)

What I do not understand is how it worked up until django<2.1 - but thats of little concern now.

Hope it checks out with you and hope to see a django 2.1.2 compatible release sometime soon.

[adamcharnock]

Closed by #42. Released in 1.9.0.