diff options
Diffstat (limited to 'lib/sqlalchemy/sql/schema.py')
| -rw-r--r-- | lib/sqlalchemy/sql/schema.py | 32 |
1 files changed, 23 insertions, 9 deletions
diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py index b7ac16b0a..08dc487d4 100644 --- a/lib/sqlalchemy/sql/schema.py +++ b/lib/sqlalchemy/sql/schema.py @@ -4087,15 +4087,29 @@ class MetaData(SchemaItem): .. warning:: - The :attr:`.sorted_tables` accessor cannot by itself accommodate - automatic resolution of dependency cycles between tables, which - are usually caused by mutually dependent foreign key constraints. - To resolve these cycles, either the - :paramref:`_schema.ForeignKeyConstraint.use_alter` - parameter may be - applied to those constraints, or use the - :func:`_schema.sort_tables_and_constraints` function which will - break out foreign key constraints involved in cycles separately. + The :attr:`.MetaData.sorted_tables` attribute cannot by itself + accommodate automatic resolution of dependency cycles between + tables, which are usually caused by mutually dependent foreign key + constraints. When these cycles are detected, the foreign keys + of these tables are omitted from consideration in the sort. + A warning is emitted when this condition occurs, which will be an + exception raise in a future release. Tables which are not part + of the cycle will still be returned in dependency order. + + To resolve these cycles, the + :paramref:`_schema.ForeignKeyConstraint.use_alter` parameter may be + applied to those constraints which create a cycle. Alternatively, + the :func:`_schema.sort_tables_and_constraints` function will + automatically return foreign key constraints in a separate + collection when cycles are detected so that they may be applied + to a schema separately. + + .. versionchanged:: 1.3.17 - a warning is emitted when + :attr:`.MetaData.sorted_tables` cannot perform a proper sort + due to cyclical dependencies. This will be an exception in a + future release. Additionally, the sort will continue to return + other tables not involved in the cycle in dependency order which + was not the case previously. .. seealso:: |