Normalize compound foreign key columns to tuples, promote tuples in docs

ForeignKey.columns and .other_columns are now tuples rather than lists,
both when introspected and when constructed directly (lists are
normalized in __post_init__). Tuples are now the documented form for
specifying compound foreign keys everywhere - in create_table()
foreign_keys=, add_foreign_key() and drop_foreign_keys=:

    foreign_keys=[(("campus_name", "dept_code"), "departments")]

Lists continue to work as input but are no longer documented.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Simon Willison 2026-07-05 15:10:21 -07:00
commit d100264e9c
5 changed files with 92 additions and 90 deletions

View file

@ -11,13 +11,13 @@ Unreleased
Breaking changes:
- ``table.foreign_keys`` now returns ``ForeignKey`` objects that are dataclasses rather than ``namedtuple`` instances, so they can no longer be unpacked or indexed as ``(table, column, other_table, other_column)`` tuples - access their fields by name instead. Compound (multi-column) foreign keys are now represented as a single ``ForeignKey`` with ``is_compound=True`` and populated ``columns``/``other_columns`` lists, where ``column`` and ``other_column`` are ``None``. Previously they were returned as one ``ForeignKey`` per column, misleadingly suggesting several independent foreign keys. See :ref:`upgrading_3_to_4` for details. (:issue:`594`)
- ``table.foreign_keys`` now returns ``ForeignKey`` objects that are dataclasses rather than ``namedtuple`` instances, so they can no longer be unpacked or indexed as ``(table, column, other_table, other_column)`` tuples - access their fields by name instead. Compound (multi-column) foreign keys are now represented as a single ``ForeignKey`` with ``is_compound=True`` and populated ``columns``/``other_columns`` tuples, where ``column`` and ``other_column`` are ``None``. Previously they were returned as one ``ForeignKey`` per column, misleadingly suggesting several independent foreign keys. See :ref:`upgrading_3_to_4` for details. (:issue:`594`)
Compound foreign key support, everywhere:
Compound foreign key support:
- Tables can now be created with compound foreign keys, by passing lists of column names in ``foreign_keys=``: ``foreign_keys=[(["campus_name", "dept_code"], "departments")]``. The referenced columns default to the compound primary key of the other table. Compound keys are rendered as table-level ``FOREIGN KEY`` constraints in the generated schema. See :ref:`python_api_compound_foreign_keys`.
- Tables can now be created with compound foreign keys, by passing tuples of column names in ``foreign_keys=``: ``foreign_keys=[(("campus_name", "dept_code"), "departments")]``. The referenced columns default to the compound primary key of the other table. Compound keys are rendered as table-level ``FOREIGN KEY`` constraints in the generated schema. See :ref:`python_api_compound_foreign_keys`.
- ``table.transform()`` now preserves compound foreign keys, applying any column renames to them. Dropping a column that is part of a compound foreign key drops the whole constraint, matching the existing single-column behavior. ``drop_foreign_keys=`` accepts a bare column name - dropping any foreign key that column participates in - or a tuple of columns to target a compound key precisely.
- ``table.add_foreign_key()`` and ``db.add_foreign_keys()`` accept lists of column names to add a compound foreign key to an existing table.
- ``table.add_foreign_key()`` and ``db.add_foreign_keys()`` accept tuples of column names to add a compound foreign key to an existing table.
- ``db.index_foreign_keys()`` creates a single composite index for a compound foreign key.
Other foreign key improvements: