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ForeignKey is now a frozen dataclass, restoring hashability

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The namedtuple-to-dataclass change made ForeignKey unhashable, breaking
set(table.foreign_keys) and dict-key usage that worked in 3.x. frozen=True
restores immutability and hashability. Equality and hashing cover all
compared fields including on_delete/on_update - two foreign keys differing
only in their actions are different constraints.

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 21:35:45 -07:00
commit 404e935b63
4 changed files with 51 additions and 8 deletions
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24
sqlite_utils/db.py
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@ -193,7 +193,7 @@ Summary information about a column, see :ref:`python_api_analyze_column`.
"""
@dataclass(order=True)
@dataclass(order=True, frozen=True)
class ForeignKey:
"""
A foreign key defined on a table.
@ -208,6 +208,11 @@ class ForeignKey:
``on_delete`` and ``on_update`` hold the foreign key actions, e.g.
``"CASCADE"`` - ``"NO ACTION"`` if not set.
Instances are immutable and hashable, so they can be collected into
sets and used as dictionary keys. Equality covers every compared field,
including ``on_delete`` and ``on_update`` - two foreign keys differing
only in their actions are different constraints.
Prior to sqlite-utils 4.0 this was a ``namedtuple`` and could be unpacked
or indexed as ``(table, column, other_table, other_column)``. It is now a
dataclass - access its fields by name instead.
@ -227,16 +232,21 @@ class ForeignKey:
def __post_init__(self):
# Populate columns/other_columns for single-column foreign keys,
# normalizing any lists to tuples
# normalizing any lists to tuples. object.__setattr__ because the
# dataclass is frozen
if self.columns:
self.columns = tuple(self.columns)
object.__setattr__(self, "columns", tuple(self.columns))
else:
self.columns = (self.column,) if self.column is not None else ()
object.__setattr__(
self, "columns", (self.column,) if self.column is not None else ()
)
if self.other_columns:
self.other_columns = tuple(self.other_columns)
object.__setattr__(self, "other_columns", tuple(self.other_columns))
else:
self.other_columns = (
(self.other_column,) if self.other_column is not None else ()
object.__setattr__(
self,
"other_columns",
(self.other_column,) if self.other_column is not None else (),
)