catch unexpected errors when accessing clslevel attribute

Improved the error message that's raised for the case where the
:func:`.association_proxy` construct attempts to access a target attribute
at the class level, and this access fails. The particular use case here is
when proxying to a hybrid attribute that does not include a working
class-level implementation.

Fixes: #7827
Change-Id: Ic6ff9df010f49253e664a1e7c7e16d8546006965

1 files changed, 7 insertions, 0 deletions

diff --git a/lib/sqlalchemy/ext/associationproxy.py b/lib/sqlalchemy/ext/associationproxy.py
index 4d2b1d8b6..194eabb64 100644
--- a/lib/sqlalchemy/ext/associationproxy.py
+++ b/lib/sqlalchemy/ext/associationproxy.py
@@ -583,6 +583,13 @@ class AssociationProxyInstance(SQLORMOperations[_T]):
             return AmbiguousAssociationProxyInstance(
                 parent, owning_class, target_class, value_attr
             )
+        except Exception as err:
+            raise exc.InvalidRequestError(
+                f"Association proxy received an unexpected error when "
+                f"trying to retreive attribute "
+                f'"{target_class.__name__}.{parent.value_attr}" from '
+                f'class "{target_class.__name__}": {err}'
+            ) from err
         else:
             return cls._construct_for_assoc(
                 target_assoc, parent, owning_class, target_class, value_attr