diff options
Diffstat (limited to 'lib/sqlalchemy/orm/relationships.py')
| -rw-r--r-- | lib/sqlalchemy/orm/relationships.py | 38 |
1 files changed, 17 insertions, 21 deletions
diff --git a/lib/sqlalchemy/orm/relationships.py b/lib/sqlalchemy/orm/relationships.py index da0730f46..552ce8b69 100644 --- a/lib/sqlalchemy/orm/relationships.py +++ b/lib/sqlalchemy/orm/relationships.py @@ -604,30 +604,26 @@ class RelationshipProperty(StrategizedProperty): and examples. :param passive_updates=True: - Indicates loading and INSERT/UPDATE/DELETE behavior when the - source of a foreign key value changes (i.e. an "on update" - cascade), which are typically the primary key columns of the - source row. + Indicates the persistence behavior to take when a referenced + primary key value changes in place, indicating that the referencing + foreign key columns will also need their value changed. - When True, it is assumed that ON UPDATE CASCADE is configured on + When True, it is assumed that ``ON UPDATE CASCADE`` is configured on the foreign key in the database, and that the database will handle propagation of an UPDATE from a source column to - dependent rows. Note that with databases which enforce - referential integrity (i.e. PostgreSQL, MySQL with InnoDB tables), - ON UPDATE CASCADE is required for this operation. The - relationship() will update the value of the attribute on related - items which are locally present in the session during a flush. - - When False, it is assumed that the database does not enforce - referential integrity and will not be issuing its own CASCADE - operation for an update. The relationship() will issue the - appropriate UPDATE statements to the database in response to the - change of a referenced key, and items locally present in the - session during a flush will also be refreshed. - - This flag should probably be set to False if primary key changes - are expected and the database in use doesn't support CASCADE - (i.e. SQLite, MySQL MyISAM tables). + dependent rows. When False, the SQLAlchemy :func:`.relationship` + construct will attempt to emit its own UPDATE statements to + modify related targets. However note that SQLAlchemy **cannot** + emit an UPDATE for more than one level of cascade. Also, + setting this flag to False is not compatible in the case where + the database is in fact enforcing referential integrity, unless + those constraints are explicitly "deferred", if the target backend + supports it. + + It is highly advised that an application which is employing + mutable primary keys keeps ``passive_updates`` set to True, + and instead uses the referential integrity features of the database + itself in order to handle the change efficiently and fully. .. seealso:: |