fix(codegen): length-prefix composite entity_id; NULL-safe; no collision#77
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…ollision Closes #44. `build_entity_id_expr` joined composite-PK columns with `'::'`. Any PK value containing `::` collapsed to a different PK's encoded form (the documented collision). Worse, on PostgreSQL `||` returns NULL for the whole expression if any operand is NULL, so any nullable composite-PK column silently broke entity_id generation. Switch to **length-prefix encoding**: each column emits `LENGTH(CAST(col AS TEXT))::text || ':' || CAST(col AS TEXT)` and the parts are concatenated with no inter-column separator. Explicit lengths disambiguate column boundaries, so distinct PK values across rows can never produce the same encoding — regardless of what characters the values contain. NULL handling: each part is wrapped in `COALESCE(..., 'N')` so NULL encodes as the literal `'N'`. Distinguishable from empty string (encodes as `'0:'`) and from values starting with `N` (those carry a length prefix). Side effect: also fixes the Postgres NULL-propagation bug. The issue recommended SHA-256 hashing. Length-prefix achieves the same "no collision risk" property using only plain SQL, no extensions (pgcrypto / SQLite hash extension) and no Postgres-version dependency. The "uniform length" property is sacrificed but isn't needed for correctness — only as an indexing hint, which isn't covered by the acceptance criteria. Tests: - `test_entity_id_expr_composite_pk`: asserts the new shape (LENGTH, COALESCE, no '::'). - `test_entity_id_expr_composite_no_separator_collision`: distinct column counts produce distinct shapes; each column gets exactly one length-prefix block; no '::' anywhere. - `test_entity_id_expr_composite_mongodb_uses_plus_concat`: MongoDB branch uses `+` (not `||`) per the existing convention. `cargo clippy --all-targets -- -D warnings` clean; 34 unit tests pass. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Summary
Per V-L2-B2: composite-PK entity_id was joining columns with
::, which collides whenever a PK value contains::, and (on Postgres) returned NULL whenever any operand was NULL.Switch to length-prefix encoding: each column emits
LENGTH(CAST(col AS TEXT))::text || '':'' || CAST(col AS TEXT)and parts are concatenated with no inter-column separator. Explicit lengths disambiguate column boundaries — no separator string can collide. NULL gets the literal'N'(distinguishable from empty string'0:'and from values starting withNwhich carry a length prefix).The issue recommended SHA-256 hashing. Length-prefix achieves the same "no collision risk" property without needing pgcrypto / SQLite hash extensions / Postgres-version dependencies. Tradeoff (no uniform output length) isn't covered by the acceptance criteria.
Closes
Test plan
cargo clippy --all-targets -- -D warningscleancargo test --lib --bins34/34 pass (2 new)test_entity_id_expr_composite_no_separator_collisionchecks distinct column counts produce distinct shapestest_entity_id_expr_composite_mongodb_uses_plus_concatkeeps MongoDB lane's+operator