base all_orm_descriptors ordering on cls.__dict__ + cls.__mro__

Adjusted the workings of the :meth:`_orm.Mapper.all_orm_descriptors`
accessor to represent the attributes in the order that they are located in
a deterministic way, assuming the use of Python 3.6 or higher which
maintains the sorting order of class attributes based on how they were
declared.   This sorting is not guaranteed to match the declared order of
attributes in all cases however; see the method documentation for the exact
scheme.

Fixes: #5494
Change-Id: I6ee8d4ace3eb8b3f7c9c0f2a3d7e27b5f62abfd3

1 files changed, 18 insertions, 6 deletions

diff --git a/lib/sqlalchemy/orm/instrumentation.py b/lib/sqlalchemy/orm/instrumentation.py
index 43e380101..f64744083 100644
--- a/lib/sqlalchemy/orm/instrumentation.py
+++ b/lib/sqlalchemy/orm/instrumentation.py
@@ -158,12 +158,24 @@ class ClassManager(HasMemoized, dict):
         :class:`.AssociationProxy`.
 
         """
-        if exclude is None:
-            exclude = set()
-        for supercls in self.class_.__mro__:
-            for key in set(supercls.__dict__).difference(exclude):
-                exclude.add(key)
-                val = supercls.__dict__[key]
+
+        found = {}
+
+        # constraints:
+        # 1. yield keys in cls.__dict__ order
+        # 2. if a subclass has the same key as a superclass, include that
+        #    key as part of the ordering of the superclass, because an
+        #    overridden key is usually installed by the mapper which is going
+        #    on a different ordering
+        # 3. don't use getattr() as this fires off descriptors
+
+        for supercls in self.class_.__mro__[0:-1]:
+            inherits = supercls.__mro__[1]
+            for key in supercls.__dict__:
+                found.setdefault(key, supercls)
+                if key in inherits.__dict__:
+                    continue
+                val = found[key].__dict__[key]
                 if (
                     isinstance(val, interfaces.InspectionAttr)
                     and val.is_attribute