Implement raiseload for deferred columns

Added "raiseload" feature for ORM mapped columns.

As part of this change, the behavior of "deferred" is now more strict;
an attribute that is set up as "deferred" at the mapper level no longer
participates in an "unexpire" operation; that is, when an unexpire loads
all the expired columns of an object which are not themselves in a deferred
group, those which are mapper-level deferred will never be loaded.

Deferral options set at query time should always be reset by an expiration
operation.

Renames deferred_scalar_loader to expired_attribute_loader

Unfortunately we can't have raiseload() do this because it would break
existing wildcard behavior.

Fixes: #4826
Change-Id: I30d9a30236e0b69134e4094fb7c1ad2267f089d1

1 files changed, 4 insertions, 3 deletions

diff --git a/lib/sqlalchemy/orm/interfaces.py b/lib/sqlalchemy/orm/interfaces.py
index 09d1858b9..abb6b14cc 100644
--- a/lib/sqlalchemy/orm/interfaces.py
+++ b/lib/sqlalchemy/orm/interfaces.py
@@ -538,9 +538,10 @@ class StrategizedProperty(MapperProperty):
             return self._strategies[key]
         except KeyError:
             cls = self._strategy_lookup(self, *key)
-            self._strategies[key] = self._strategies[cls] = strategy = cls(
-                self, key
-            )
+            # this previosuly was setting self._strategies[cls], that's
+            # a bad idea; should use strategy key at all times because every
+            # strategy has multiple keys at this point
+            self._strategies[key] = strategy = cls(self, key)
             return strategy
 
     def setup(self, context, query_entity, path, adapter, **kwargs):