Remove session.flush() and session.query() monkey patching

Use custom Session class to avoid monkey patching of SqlAlchemy
Session instance.

blueprint db-session-cleanup

Change-Id: I7d40c20e585782403556f3587141805c197bfa64

2 files changed, 12 insertions, 9 deletions

diff --git a/nova/db/sqlalchemy/session.py b/nova/db/sqlalchemy/session.py
index b128ccc23..ae8fec32d 100644
--- a/nova/db/sqlalchemy/session.py
+++ b/nova/db/sqlalchemy/session.py
@@ -306,7 +306,6 @@ def get_session(autocommit=True, expire_on_commit=False):
         _MAKER = get_maker(engine, autocommit, expire_on_commit)
 
     session = _MAKER()
-    session = wrap_session(session)
     return session
 
 
@@ -388,13 +387,6 @@ def wrap_db_error(f):
     return _wrap
 
 
-def wrap_session(session):
-    """Return a session whose exceptions are wrapped."""
-    session.query = wrap_db_error(session.query)
-    session.flush = wrap_db_error(session.flush)
-    return session
-
-
 def get_engine():
     """Return a SQLAlchemy engine."""
     global _ENGINE
@@ -548,9 +540,21 @@ class Query(sqlalchemy.orm.query.Query):
                            synchronize_session=synchronize_session)
 
 
+class Session(sqlalchemy.orm.session.Session):
+    """Custom Session class to avoid SqlAlchemy Session monkey patching"""
+    @wrap_db_error
+    def query(self, *args, **kwargs):
+        return super(Session, self).query(*args, **kwargs)
+
+    @wrap_db_error
+    def flush(self, *args, **kwargs):
+        return super(Session, self).flush(*args, **kwargs)
+
+
 def get_maker(engine, autocommit=True, expire_on_commit=False):
     """Return a SQLAlchemy sessionmaker using the given engine."""
     return sqlalchemy.orm.sessionmaker(bind=engine,
+                                       class_=Session,
                                        autocommit=autocommit,
                                        expire_on_commit=expire_on_commit,
                                        query_cls=Query)
diff --git a/nova/virt/baremetal/db/sqlalchemy/session.py b/nova/virt/baremetal/db/sqlalchemy/session.py
index 3e562e32a..29d77c2a0 100644
--- a/nova/virt/baremetal/db/sqlalchemy/session.py
+++ b/nova/virt/baremetal/db/sqlalchemy/session.py
@@ -47,7 +47,6 @@ def get_session(autocommit=True, expire_on_commit=False):
         _MAKER = nova_session.get_maker(engine, autocommit, expire_on_commit)
 
     session = _MAKER()
-    session = nova_session.wrap_session(session)
     return session