Add legacy get_sessionmaker() method

Some projects are calling EngineFacade._session_maker for
some use cases.  To suit these cases more cleanly on the legacy
API, add a public get_sessionmaker() method.

Change-Id: Ica9574d70a6b8be80bd1a5e7cf250828455c5ade

2 files changed, 19 insertions, 0 deletions

diff --git a/oslo_db/sqlalchemy/enginefacade.py b/oslo_db/sqlalchemy/enginefacade.py
index 056dd31..4497a50 100644
--- a/oslo_db/sqlalchemy/enginefacade.py
+++ b/oslo_db/sqlalchemy/enginefacade.py
@@ -964,6 +964,18 @@ class LegacyEngineFacade(object):
         else:
             return self._factory._writer_maker(**kwargs)
 
+    def get_sessionmaker(self, use_slave=False):
+        """Get the sessionmaker instance used to create a Session.
+
+        This can be called for those cases where the sessionmaker() is to
+        be temporarily injected with some state such as a specific connection.
+
+        """
+        if use_slave:
+            return self._factory._reader_maker
+        else:
+            return self._factory._writer_maker
+
     @classmethod
     def from_config(cls, conf,
                     sqlite_fk=False, autocommit=True, expire_on_commit=False):
diff --git a/oslo_db/tests/sqlalchemy/test_enginefacade.py b/oslo_db/tests/sqlalchemy/test_enginefacade.py
index a463c7b..fe8030c 100644
--- a/oslo_db/tests/sqlalchemy/test_enginefacade.py
+++ b/oslo_db/tests/sqlalchemy/test_enginefacade.py
@@ -947,6 +947,13 @@ class LegacyIntegrationtest(test_base.DbTestCase):
             enginefacade.get_legacy_facade() is legacy_facade
         )
 
+    def test_get_sessionmaker(self):
+        legacy_facade = enginefacade.get_legacy_facade()
+        self.assertTrue(
+            legacy_facade.get_sessionmaker() is
+            enginefacade._context_manager._factory._writer_maker
+        )
+
 
 class ThreadingTest(test_base.DbTestCase):
     """Test copying on new threads using real connections and sessions."""