Fixes for table-bound version_id_col against mapped selectable

Fixed bug where a versioning column specified on a mapper against a
:func:`.select` construct where the version_id_col itself were against the
underlying table would incur additional loads when accessed, even if the
value were locally persisted by the flush.  The actual fix is a result of
the changes in :ticket:`4617`,  by fact that a :func:`.select` object no
longer has a ``.c`` attribute and therefore does not confuse the mapper
into thinking there's an unknown column value present.

Fixed bug in ORM versioning feature where assignment of an explicit
version_id for a counter configured against a mapped selectable where
version_id_col is against the underlying table would fail if the previous
value were expired; this was due to the fact that the  mapped attribute
would not be configured with active_history=True.

Fixes: #4194
Fixes: #4195
Change-Id: I214879f441f905bdd85a7411f90352af7399051d

1 files changed, 5 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/strategies.py b/lib/sqlalchemy/orm/strategies.py
index 79e36026c..9abb5be40 100644
--- a/lib/sqlalchemy/orm/strategies.py
+++ b/lib/sqlalchemy/orm/strategies.py
@@ -198,7 +198,11 @@ class ColumnLoader(LoaderStrategy):
         active_history = (
             self.parent_property.active_history
             or self.columns[0].primary_key
-            or mapper.version_id_col in set(self.columns)
+            or (
+                mapper.version_id_col is not None
+                and mapper._columntoproperty.get(mapper.version_id_col, None)
+                is self.parent_property
+            )
         )
 
         _register_attribute(