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| -rw-r--r-- | doc/build/orm/mapper_config.rst | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/doc/build/orm/mapper_config.rst b/doc/build/orm/mapper_config.rst index 22f483c7e..2cf61d06c 100644 --- a/doc/build/orm/mapper_config.rst +++ b/doc/build/orm/mapper_config.rst @@ -1395,6 +1395,16 @@ each time an ``UPDATE`` to the mapped table occurs. This value is checked each time the ORM emits an ``UPDATE`` or ``DELETE`` against the row to ensure that the value held in memory matches the database value. +.. warning:: + + Because the versioning feature relies upon comparison of the **in memory** + record of an object, the feature only applies to the :meth:`.Session.flush` + process, where the ORM flushes individual in-memory rows to the database. + It does **not** take effect when performing + a multirow UPDATE or DELETE using :meth:`.Query.update` or :meth:`.Query.delete` + methods, as these methods only emit an UPDATE or DELETE statement but otherwise + do not have direct access to the contents of those rows being affected. + The purpose of this feature is to detect when two concurrent transactions are modifying the same row at roughly the same time, or alternatively to provide a guard against the usage of a "stale" row in a system that might be re-using |