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add_foreign_keys() errors instead of silently dropping action changes

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The existing-foreign-key dedup compared only columns and other_table, so
requesting an FK that already exists with different ON DELETE/ON UPDATE
actions was a silent no-op - and with add_foreign_key() raising "already
exists", there was no signal that the requested actions were dropped.
An exact match (including actions) is still skipped for idempotency;
a mismatch now raises AlterError pointing at table.transform().

Also validates that compound foreign keys passed as 4-tuples have the
same number of columns on both sides - extra other-columns were being
silently discarded, e.g. ("t", ("a",), "other", ("a", "b")) created a
single-column key referencing just "a".

Refs https://github.com/simonw/sqlite-utils/issues/769#issuecomment-4900034150

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Simon Willison 2026-07-06 21:53:48 -07:00
commit 16bbfb582d
4 changed files with 71 additions and 3 deletions
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46
tests/test_foreign_keys.py
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@ -643,3 +643,49 @@ def test_create_table_mixed_foreign_keys_with_string(fresh_db):
)
fks = {fk.column: fk.other_table for fk in fresh_db["books"].foreign_keys}
assert fks == {"author_id": "authors", "publisher_id": "publishers"}
def test_add_foreign_keys_existing_with_different_actions_errors(fresh_db):
# Requesting an existing foreign key with different ON DELETE/ON UPDATE
# actions was silently skipped, dropping the requested change
fresh_db["authors"].insert({"id": 1}, pk="id")
fresh_db["books"].insert(
{"id": 1, "author_id": 1},
pk="id",
foreign_keys=[("author_id", "authors", "id")],
)
with pytest.raises(AlterError) as ex:
fresh_db.add_foreign_keys(
[ForeignKey("books", "author_id", "authors", "id", on_delete="CASCADE")]
)
assert "ON DELETE" in str(ex.value)
assert fresh_db["books"].foreign_keys[0].on_delete == "NO ACTION"
def test_add_foreign_keys_identical_existing_is_noop(fresh_db):
# An exact match, including actions, is silently skipped so repeated
# calls stay idempotent
fresh_db["authors"].insert({"id": 1}, pk="id")
fresh_db["books"].insert({"id": 1, "author_id": 1}, pk="id")
fresh_db["books"].add_foreign_key("author_id", "authors", "id", on_delete="CASCADE")
fresh_db.add_foreign_keys(
[ForeignKey("books", "author_id", "authors", "id", on_delete="CASCADE")]
)
fks = fresh_db["books"].foreign_keys
assert len(fks) == 1
assert fks[0].on_delete == "CASCADE"
def test_add_foreign_keys_compound_column_count_mismatch_errors(fresh_db):
# Previously the extra other-column was silently discarded, creating
# a single-column foreign key to just ("id")
fresh_db["departments"].insert(
{"campus": "north", "code": "cs"}, pk=("campus", "code")
)
fresh_db["courses"].insert({"id": 1, "campus": "north"}, pk="id")
with pytest.raises(ValueError) as ex:
fresh_db.add_foreign_keys(
[("courses", ("campus",), "departments", ("campus", "code"))]
)
assert "same number of columns" in str(ex.value)
assert fresh_db["courses"].foreign_keys == []