ensure MappedColumn col is mapped under alternate key

Fixes: #8025
Change-Id: I83ba54f05bd2e5fc87d80f42fbeb6d4d2f2ac5fa

1 files changed, 14 insertions, 7 deletions

diff --git a/lib/sqlalchemy/orm/decl_base.py b/lib/sqlalchemy/orm/decl_base.py
index b1f81cb6b..fe5a20d04 100644
--- a/lib/sqlalchemy/orm/decl_base.py
+++ b/lib/sqlalchemy/orm/decl_base.py
@@ -876,20 +876,27 @@ class _ClassScanMapperConfig(_MapperConfig):
         name_to_prop_key = collections.defaultdict(set)
         for key, c in list(our_stuff.items()):
             if isinstance(c, _MapsColumns):
-                for col in c.columns_to_assign:
-                    if not isinstance(c, Composite):
-                        name_to_prop_key[col.name].add(key)
-                    declared_columns.add(col)
 
-                # remove object from the dictionary that will be passed
-                # as mapper(properties={...}) if it is not a MapperProperty
-                # (i.e. this currently means it's a MappedColumn)
                 mp_to_assign = c.mapper_property_to_assign
                 if mp_to_assign:
                     our_stuff[key] = mp_to_assign
                 else:
+                    # if no mapper property to assign, this currently means
+                    # this is a MappedColumn that will produce a Column for us
                     del our_stuff[key]
 
+                for col in c.columns_to_assign:
+                    if not isinstance(c, Composite):
+                        name_to_prop_key[col.name].add(key)
+                    declared_columns.add(col)
+
+                    # if this is a MappedColumn and the attribute key we
+                    # have is not what the column has for its key, map the
+                    # Column explicitly under the attribute key name.
+                    # otherwise, Mapper will map it under the column key.
+                    if mp_to_assign is None and key != col.key:
+                        our_stuff[key] = col
+
             elif isinstance(c, Column):
                 # undefer previously occurred here, and now occurs earlier.
                 # ensure every column we get here has been named