From d9af0892dc2b822446d0a0168ece606d8975e175 Mon Sep 17 00:00:00 2001
From: Kevin Benton <kevin@benton.pub>
Date: Wed, 15 Feb 2017 10:15:39 -0800
Subject: [PATCH] Load all eager relationships on 'before_commit' event

This event handler will ensure that all eagerly loaded
relationships are loaded on a newly created sqla object.
This will allow us to continue our pattern of calling
make_whatever_dict outside of the transaction context
manager after the switch to the new engine facade
managers.

Co-Authored-By: Mike Bayer <mike_mp@zzzcomputing.com>
Partially-Implements: blueprint enginefacade-switch
Change-Id: I144fed595a740c29fe58ec75fe8dd0a1f1ca4523
---
 neutron/db/api.py                             | 31 +++++++++++++++++++
 .../tests/unit/db/test_db_base_plugin_v2.py   |  9 ++++++
 2 files changed, 40 insertions(+)

diff --git a/neutron/db/api.py b/neutron/db/api.py
index 5168dd0957f..00ae61bca9d 100644
--- a/neutron/db/api.py
+++ b/neutron/db/api.py
@@ -31,6 +31,7 @@ import six
 import sqlalchemy
 from sqlalchemy import event  # noqa
 from sqlalchemy import exc as sql_exc
+from sqlalchemy import orm
 from sqlalchemy.orm import exc
 
 from neutron._i18n import _LE
@@ -261,3 +262,33 @@ def sqla_remove_all():
             # already removed
             pass
     del _REGISTERED_SQLA_EVENTS[:]
+
+
+@event.listens_for(orm.session.Session, "before_commit")
+def load_one_to_manys(session):
+    # TODO(kevinbenton): we should be able to remove this after we
+    # have eliminated all places where related objects are constructed
+    # using a key rather than a relationship.
+    for new_object in session.new:
+        state = sqlalchemy.inspect(new_object)
+
+        # set up relationship loading so that we can call lazy
+        # loaders on the object even though the ".key" is not set up yet
+        # (normally happens by in after_flush_postexec, but we're trying
+        # to do this more succinctly).  in this context this is only
+        # setting a simple flag on the object's state.
+        session.enable_relationship_loading(new_object)
+
+        # look for eager relationships and do normal load.
+        # For relationships where the related object is also
+        # in the session these lazy loads will pull from the
+        # identity map and not emit SELECT.  Otherwise, we are still
+        # local in the transaction so a normal SELECT load will work fine.
+        for relationship_attr in state.mapper.relationships:
+            if relationship_attr.lazy not in ('joined', 'subquery'):
+                # we only want to automatically load relationships that would
+                # automatically load during a lookup operation
+                continue
+            if relationship_attr.key not in state.dict:
+                getattr(new_object, relationship_attr.key)
+                assert relationship_attr.key in state.dict
diff --git a/neutron/tests/unit/db/test_db_base_plugin_v2.py b/neutron/tests/unit/db/test_db_base_plugin_v2.py
index 9ba965cd3b3..fb261d313f6 100644
--- a/neutron/tests/unit/db/test_db_base_plugin_v2.py
+++ b/neutron/tests/unit/db/test_db_base_plugin_v2.py
@@ -6061,6 +6061,15 @@ class TestSubnetPoolsV2(NeutronDbPluginV2TestCase):
 
 class DbModelMixin(object):
     """DB model tests."""
+    def test_make_network_dict_outside_engine_facade_manager(self):
+        ctx = context.get_admin_context()
+        with db_api.context_manager.writer.using(ctx):
+            network = models_v2.Network(name="net_net", status="OK",
+                                        admin_state_up=True)
+            ctx.session.add(network)
+        pl = db_base_plugin_common.DbBasePluginCommon()
+        self.assertFalse(pl._make_network_dict(network, context=ctx)['shared'])
+
     def test_repr(self):
         """testing the string representation of 'model' classes."""
         network = models_v2.Network(name="net_net", status="OK",