Use class-local metadata for declarative base

Fixed regression where the ``.metadata`` attribute on a per class level
would not be honored, breaking the use case of per-class-hierarchy
:class:`.schema.MetaData` for abstract declarative classes and mixins.

Fixes: #6128
Change-Id: I5c15436b5c5171105dc1a0192fa744daf79a344d

1 files changed, 7 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/decl_base.py b/lib/sqlalchemy/orm/decl_base.py
index e55056fdf..5a5d98a95 100644
--- a/lib/sqlalchemy/orm/decl_base.py
+++ b/lib/sqlalchemy/orm/decl_base.py
@@ -783,7 +783,7 @@ class _ClassScanMapperConfig(_MapperConfig):
                     "__table__",
                     table_cls(
                         tablename,
-                        manager.registry.metadata,
+                        self._metadata_for_cls(manager),
                         *(tuple(declared_columns) + tuple(args)),
                         **table_kw
                     ),
@@ -800,6 +800,12 @@ class _ClassScanMapperConfig(_MapperConfig):
                         )
         self.local_table = table
 
+    def _metadata_for_cls(self, manager):
+        if hasattr(self.cls, "metadata"):
+            return self.cls.metadata
+        else:
+            return manager.registry.metadata
+
     def _setup_inheritance(self, mapper_kw):
         table = self.local_table
         cls = self.cls