# ADR-032 — Person-delete referential integrity lives in the database, and the cascade never reaches `documents`

**Date:** 2026-06-06
**Status:** Accepted
**Issue:** #684 (move person-delete FK detach to database-level `ON DELETE`)
**Milestone:** —

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## Context

Deleting a `Person` had to detach the two FKs into `persons` that lacked any `ON DELETE`
behaviour: `documents.sender_id` and `document_receivers.person_id` (both from V1).
`PersonService.deletePerson` and `mergePersons` did this in Java — nulling the sender and
deleting receiver join rows before `deleteById` — so the integrity guarantee lived in
application code. Any other delete path (a future endpoint, a manual `psql`, a batch job)
could still orphan rows or fail with an FK-violation 500.

A related soft reference made it worse: `transcription_block_mentioned_persons.person_id`
was a UUID column with **no FK** (V56, a deliberate "no FK" choice), so a person delete left
dangling `@`-mention rows. The literal `@DisplayName` lives in `transcription_blocks.text`,
so only the *link* was ever at stake — not the visible name.

## Decision

Move person-delete integrity into the database (migration V71) and thin the service to a
plain `deleteById`:

- `documents.sender_id` → `ON DELETE SET NULL` (`documents.senderText` preserves the raw
  textual attribution, so nulling the link loses no historical record).
- `document_receivers.person_id` → `ON DELETE CASCADE` (the symmetric completion of V14,
  which gave the `document_id` side the same).
- `transcription_block_mentioned_persons.person_id` → a real FK with `ON DELETE CASCADE`,
  reversing V56's "no FK" decision. The read renderer already degrades a `@DisplayName` with
  no sidecar row to plain escaped text, so removing the link is invisible to the reader.

**Cascade-boundary invariant:** the cascade stays strictly at the join/reference layer and
**never reaches `documents` rows** — a cascade into `documents` would destroy historical
letters. This is pinned by a non-negotiable document-survival assertion in
`PersonRepositoryTest`.

## Consequences

- A person delete is safe from every path, not just `PersonService`. The service and merge
  stay thin (`deleteById` + the cascade); `reassignSenderToNull` and `deleteReceiverReferences`
  are deleted.
- This *fixes* the pre-existing dead-link-on-deleted-person case — it is not a purely
  invisible refactor. Note the read renderer strips the `@` prefix when it emits a live
  mention link, but the degraded (deleted-person) path leaves the literal `@Name` in the
  block text as-is — the reader sees `@Auguste Raddatz` as plain text, never a dead link.
- DB cascades run below `AuditService`, so the row-level cleanup is intentionally not
  audit-logged; the person-delete action itself is still logged at the service layer.
- The V71 FK validation requires cleaning pre-existing orphan mention rows first; the
  migration does this in a `DO` block that logs the purge count via `RAISE NOTICE`.

## Alternatives considered

- **Keep integrity in Java** — rejected; it only protects the one code path and re-breaks the
  moment a second delete path appears.
- **Cascade `documents.sender_id`** — rejected; it would delete historical letters when a
  sender is removed. `SET NULL` keeps the letter and its `senderText`.
- **Leave the mention sidecar FK-less (honour V56)** — rejected; the "no FK" rationale was
  stale, the name survives in the block text regardless, and the FK removes the orphan-row
  class of bug.
