1 files changed, 15 insertions, 6 deletions
diff --git a/keystone/common/sql/migrations/env.py b/keystone/common/sql/migrations/env.py
index 2d116f1bd..f5547a4e4 100644
--- a/keystone/common/sql/migrations/env.py
+++ b/keystone/common/sql/migrations/env.py
@@ -59,15 +59,24 @@ def run_migrations_online():
     In this scenario we need to create an Engine and associate a connection
     with the context.
     """
-    connectable = engine_from_config(
-        config.get_section(config.config_ini_section),
-        prefix="sqlalchemy.",
-        poolclass=pool.NullPool,
-    )
+    connectable = config.attributes.get('connection', None)
+
+    if connectable is None:
+        # only create Engine if we don't have a Connection from the outside
+        connectable = engine_from_config(
+            config.get_section(config.config_ini_section),
+            prefix="sqlalchemy.",
+            poolclass=pool.NullPool,
+        )
+
+    # when connectable is already a Connection object, calling connect() gives
+    # us a *branched connection*.
 
     with connectable.connect() as connection:
         context.configure(
-            connection=connection, target_metadata=target_metadata
+            connection=connection,
+            target_metadata=target_metadata,
+            render_as_batch=True,
         )
 
         with context.begin_transaction():