Every deletion of a Vertragsänderung failed with "new row for relation
employees violates check constraint chk_weekly_hours". The revert wrote
one UPDATE per field, and chk_weekly_hours ties two of them together:
Vollzeit means exactly 38.5 hours, Teilzeit means something in between.
Setting the employment type back to Vollzeit while 37 hours still stood
produced precisely the state the constraint forbids. It hit nearly every
contract change, because the form changes those two together.
Collecting the assignments and writing them in a single UPDATE removes
the intermediate state entirely. The state being restored was valid once
— it is in the history because it was — so restoring it whole is safe.
A violation can still be real: if a later change touched one of a
coupled pair on its own, the old value no longer fits today's state.
That case is caught and reported as a sentence instead of surfacing a
database error in a toast.
My tests did not catch this, and could not have: the revert lives in SQL
and the suite has no way to run it. What did catch it was HR clicking
the button. The rehearsal script now covers the reported case, an
unrelated single-field revert, and the genuine conflict.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
