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Primary and foreign keys are already first-class in Modelith — a PK is a `pk` KeyGroup with ordered members (composite-capable), an FK is a Relationship whose from/to ends carry paired attribute lists (multi-column-capable). This closes the two validation gaps that model left open: - MDL-W115 (warning): a PK KeyGroup member marked `nullable: true` — a primary key must not be null. A warning, not an error, so legacy models built on the `role: business_key` convention (which carried no nullability contract) don't suddenly fail. - MDL-E114 (error): a foreign key whose paired from/to attributes have mismatched domains — a join that can never work. Only compares when both ends are column-mapped 1:1 and both declare a domain. Deliberately NOT adding a `role: primary_key`/`foreign_key` + `references:` attribute syntax (as the issue proposed): it would be a second, weaker source of truth for the same fact and couldn't express composite keys or multi-column FKs cleanly. The existing KeyGroup/Relationship model already covers the issue's desired effects (validation, dbt constraints/tests, ERD cardinality). Tests: test_key_constraints.py (nullable/composite PK, FK match/mismatch/missing- domain/unmapped). 561 passed, 1 skipped; ruff clean; verified on the CLI. Spec §2.4 documents the codes and the design rationale.
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Primary and foreign keys are already first-class in Modelith — a PK is a
pkKeyGroup with ordered members (composite-capable), an FK is a Relationship whose from/to ends carry paired attribute lists (multi-column-capable). This closes the two validation gaps that model left open:nullable: true— a primary key must not be null. A warning, not an error, so legacy models built on therole: business_keyconvention (which carried no nullability contract) don't suddenly fail.Deliberately NOT adding a
role: primary_key/foreign_key+references:attribute syntax (as the issue proposed): it would be a second, weaker source of truth for the same fact and couldn't express composite keys or multi-column FKs cleanly. The existing KeyGroup/Relationship model already covers the issue's desired effects (validation, dbt constraints/tests, ERD cardinality).Tests: test_key_constraints.py (nullable/composite PK, FK match/mismatch/missing- domain/unmapped). 561 passed, 1 skipped; ruff clean; verified on the CLI. Spec §2.4 documents the codes and the design rationale.
What this changes
How it was tested
Checklist
uv run pytest)uv run ruff check packages/)