Fix statesman index detection

[hmarr]

The previous logic worked fine with parent tables that (approximately) began with the letters A-S, but with tables that (approximately) started with the letters T-Z, the comparison would fail, which ultimately resulted in the RecordNotUnique exception not being converted to a TransitionConflictError. Among other things, this prevents retry_conflicts from working.

[hmarr]

Looks like the mongo tests are failing due to rails/rails#35153 (unrelated), and have been failing consistently for the past few builds.

[lawrencejones]

Can we add a quick test that catches this? I can see that .sort going missing in a refactor later.

Might also be worth a small comment on the comparison that says we don't care about the index columns ordering as we only care about the uniqueness property? At first this looked wrong to me as I'm so used to index column ordering being integral to the index behaviour, but of course this doesn't matter when we just care about uniqueness.

Nice catch though!

[hmarr]

Adding a test is a little tricky as the column name comes from the test model we use everywhere (MyActiveRecordModel). I did briefly consider renaming it to ZyActiveRecordModel but figured that'd confuse a lot of people 🤠 If you have any ideas on how we can easily test this without lots of stubbing and testing of private methods, I'm all ears! But it'd be great to get this fix in soon as we're seeing a lot of exceptions because of it :-)

Good shout on the comment - added!

[lawrencejones]

If it's not easy to add in a sensible way then let's get this merged. It's not like we're unclear on the nature of the issue or uncertain that this will fix it.

If you can rebase then I can merge and cut a new release?

[hmarr]

Thanks 🙌

Just rebased and pushed.

[lawrencejones]

This should now be released in v4.1.1

[hmarr]

Thanks Lawrence!