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

6 files changed, 193 insertions, 2 deletions

diff --git a/doc/build/changelog/unreleased_14/6128.rst b/doc/build/changelog/unreleased_14/6128.rst
new file mode 100644
index 000000000..5eb7f4a6f
--- /dev/null
+++ b/doc/build/changelog/unreleased_14/6128.rst
@@ -0,0 +1,12 @@
+.. change::
+    :tags: bug, regression, orm, declarative
+    :tickets: 6128
+
+    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.
+
+
+    .. seealso::
+
+      :ref:`declarative_metadata`
\ No newline at end of file
diff --git a/doc/build/orm/declarative_config.rst b/doc/build/orm/declarative_config.rst
index 48c270b4e..8e3bc5882 100644
--- a/doc/build/orm/declarative_config.rst
+++ b/doc/build/orm/declarative_config.rst
@@ -240,6 +240,74 @@ configuration via the :meth:`.MapperEvents.before_configured` event::
 
 .. versionadded:: 0.9.3
 
+
+.. _declarative_metadata:
+
+``metadata``
+~~~~~~~~~~~~
+
+The :class:`_schema.MetaData` collection normally used to assign a new
+:class:`_schema.Table` is the :attr:`_orm.registry.metadata` attribute
+associated with the :class:`_orm.registry` object in use. When using a
+declarative base class such as that generated by :func:`_orm.declarative_base`
+as well as :meth:`_orm.registry.generate_base`, this :class:`_schema.MetaData`
+is also normally present also as an attribute named ``.metadata`` that's
+directly on the base class, and thus also on the mapped class via
+inheritance.    Declarative uses this attribute, when present, in order to
+determine the target :class:`_schema.MetaData` collection, or if not
+present, uses the :class:`_schema.MetaData` associated directly with the
+:class:`_orm.registry`.
+
+This attribute may also be assigned towards in order to affect the
+:class:`_schema.MetaData` collection to be used on a per-mapped-hierarchy basis
+for a single base and/or :class:`_orm.registry`. This takes effect whether a
+declarative base class is used or if the :meth:`_orm.registry.mapped` decorator
+is used directly, thus allowing patterns such as the metadata-per-abstract base
+example in the next section, :ref:`declarative_abstract`. A similar pattern can
+be illustrated using :meth:`_orm.registry.mapped` as follows::
+
+    reg = registry()
+
+    class BaseOne:
+        metadata = MetaData()
+
+    class BaseTwo:
+        metadata = MetaData()
+
+    @reg.mapped
+    class ClassOne:
+        __tablename__ = 't1'  # will use reg.metadata
+
+        id = Column(Integer, primary_key=True)
+
+    @reg.mapped
+    class ClassTwo(BaseOne):
+        __tablename__ = 't1'  # will use BaseOne.metadata
+
+        id = Column(Integer, primary_key=True)
+
+    @reg.mapped
+    class ClassThree(BaseOne):
+        __tablename__ = 't1'  # will use BaseTwo.metadata
+
+        id = Column(Integer, primary_key=True)
+
+
+.. versionchanged:: 1.4.3  The :meth:`_orm.registry.mapped` decorator will
+   honor an attribute named ``.metadata`` on the class as an alternate
+   :class:`_schema.MetaData` collection to be used in place of the
+   :class:`_schema.MetaData` that's on the :class:`_orm.registry` itself.
+   This matches the behavior of the base class returned by the
+   :meth:`_orm.registry.generate_base` and :meth:`_orm.declarative_base`
+   method/function.  Note this feature was broken due to a regression in
+   1.4.0, 1.4.1 and 1.4.2, even when using :func:`_orm.declarative_base`;
+   1.4.3 is needed to restore the behavior.
+
+
+.. seealso::
+
+    :ref:`declarative_abstract`
+
 .. _declarative_abstract:
 
 ``__abstract__``
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
diff --git a/test/aaa_profiling/test_memusage.py b/test/aaa_profiling/test_memusage.py
index b1dd29a7e..d8896a3d6 100644
--- a/test/aaa_profiling/test_memusage.py
+++ b/test/aaa_profiling/test_memusage.py
@@ -341,7 +341,7 @@ class MemUsageTest(EnsureZeroed):
 class MemUsageWBackendTest(EnsureZeroed):
 
     __tags__ = ("memory_intensive",)
-    __requires__ = "cpython", "memory_process_intensive"
+    __requires__ = "cpython", "memory_process_intensive", "no_asyncio"
     __sparse_backend__ = True
 
     # ensure a pure growing test trips the assertion
diff --git a/test/orm/declarative/test_mixin.py b/test/orm/declarative/test_mixin.py
index ad4832c35..05628641a 100644
--- a/test/orm/declarative/test_mixin.py
+++ b/test/orm/declarative/test_mixin.py
@@ -243,6 +243,104 @@ class DeclarativeMixinTest(DeclarativeTestBase):
 
         eq_(Manager.__table__.name, "manager")
 
+    def test_same_base_multiple_metadata(self):
+        m1 = MetaData()
+        m2 = MetaData()
+
+        class B1(Base):
+            __abstract__ = True
+            metadata = m1
+
+        class B2(Base):
+            __abstract__ = True
+            metadata = m2
+
+            def fullname(self):
+                return self.name + " " + self.surname
+
+        class User(B1):
+            __tablename__ = "user"
+
+            id = Column(Integer, primary_key=True)
+            name = Column(String)
+            surname = Column(String)
+
+        class AD(B1):
+            __tablename__ = "address"
+
+            id = Column(Integer, primary_key=True)
+
+        class OtherUser(B2):
+            __tablename__ = "user"
+
+            id = Column(Integer, primary_key=True)
+            username = Column(String)
+
+        class BUser(Base):
+            __tablename__ = "user"
+
+            id = Column(Integer, primary_key=True)
+            login = Column(String)
+
+        eq_(set(m1.tables), {"user", "address"})
+        eq_(set(m2.tables), {"user"})
+        eq_(set(Base.registry.metadata.tables), {"user"})
+
+        eq_(Base.registry.metadata.tables["user"].c.keys(), ["id", "login"])
+        eq_(m1.tables["user"].c.keys(), ["id", "name", "surname"])
+        eq_(m2.tables["user"].c.keys(), ["id", "username"])
+
+    def test_same_registry_multiple_metadata(self):
+        m1 = MetaData()
+        m2 = MetaData()
+
+        reg = registry()
+
+        class B1(object):
+            metadata = m1
+
+        class B2(object):
+            metadata = m2
+
+            def fullname(self):
+                return self.name + " " + self.surname
+
+        @reg.mapped
+        class User(B1):
+            __tablename__ = "user"
+
+            id = Column(Integer, primary_key=True)
+            name = Column(String)
+            surname = Column(String)
+
+        @reg.mapped
+        class AD(B1):
+            __tablename__ = "address"
+
+            id = Column(Integer, primary_key=True)
+
+        @reg.mapped
+        class OtherUser(B2):
+            __tablename__ = "user"
+
+            id = Column(Integer, primary_key=True)
+            username = Column(String)
+
+        @reg.mapped
+        class BUser(object):
+            __tablename__ = "user"
+
+            id = Column(Integer, primary_key=True)
+            login = Column(String)
+
+        eq_(set(m1.tables), {"user", "address"})
+        eq_(set(m2.tables), {"user"})
+        eq_(set(reg.metadata.tables), {"user"})
+
+        eq_(reg.metadata.tables["user"].c.keys(), ["id", "login"])
+        eq_(m1.tables["user"].c.keys(), ["id", "name", "surname"])
+        eq_(m2.tables["user"].c.keys(), ["id", "username"])
+
     def test_not_allowed(self):
         class MyMixin:
             foo = Column(Integer, ForeignKey("bar.id"))
diff --git a/test/requirements.py b/test/requirements.py
index df4a3b601..27bf17c0a 100644
--- a/test/requirements.py
+++ b/test/requirements.py
@@ -1458,6 +1458,13 @@ class DefaultRequirements(SuiteRequirements):
         )
 
     @property
+    def no_asyncio(self):
+        def go(config):
+            return config.db.dialect.is_async
+
+        return skip_if(go)
+
+    @property
     def no_mssql_freetds(self):
         return self.mssql_freetds.not_()