Add QueryableAttribute._impl_uses_objects accessor for AssociationProxy

Fixed regression where new association proxy system was still not proxying
hybrid attributes when they made use of the ``@hybrid_property.expression``
decorator to return an alternate SQL expression, or when the hybrid
returned an arbitrary :class:`.PropComparator`, at the expression level.
This involved futher generalization of the heuristics used to detect the
type of object being proxied at the level of :class:`.QueryableAttribute`,
to better detect if the descriptor ultimately serves mapped classes or
column expressions.

Fixes: #4690
Change-Id: I5b5300661291c94a23de53bcf92d747701720aa1

1 files changed, 11 insertions, 0 deletions

diff --git a/lib/sqlalchemy/orm/attributes.py b/lib/sqlalchemy/orm/attributes.py
index f37928cc1..674c57fea 100644
--- a/lib/sqlalchemy/orm/attributes.py
+++ b/lib/sqlalchemy/orm/attributes.py
@@ -104,6 +104,10 @@ class QueryableAttribute(
     def _supports_population(self):
         return self.impl.supports_population
 
+    @property
+    def _impl_uses_objects(self):
+        return self.impl.uses_objects
+
     def get_history(self, instance, passive=PASSIVE_OFF):
         return self.impl.get_history(
             instance_state(instance), instance_dict(instance), passive
@@ -310,6 +314,13 @@ def create_proxied_attribute(descriptor):
         _is_internal_proxy = True
 
         @property
+        def _impl_uses_objects(self):
+            return (
+                self.original_property is not None
+                and getattr(self.class_, self.key).impl.uses_objects
+            )
+
+        @property
         def property(self):
             return self.comparator.property