fix(config): Throw PreconditionException always when it didn't match

[nickvergessen]

Summary

Explanation	Screenshot
Previously even when the precondition did not match, the call "passed" when the after value was the expected one. This however can lead to race conditions, duplicate code executions and other things.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[come-nc]

Does this make any sense without a transaction or a lock around it anyway? What prevents the DB value to be changed by another process between precondition check and value update?

[nickvergessen]

What prevents the DB value to be changed by another process between precondition check and value update?

There is another check inside that takes care of it (no changed row while the precondition is in the WHERE clause):

server/lib/private/DB/Connection.php

Lines 620 to 622 in edaa4d1

	if ($affected === 0 && !empty($updatePreconditionValues)) {
	throw new PreConditionNotMetException();
	}

[nickvergessen]

/backport to stable30

[nickvergessen]

/backport to stable29

[nickvergessen]

/backport to stable28