Speed up loading a change with eager loading

To display a change screen, we need to access all of the revisions,
files, and comments for the change.  Tell SQLAlchemy in that case
to go ahead and load everything in one query.  In local testing,
this made https://review.openstack.org/223333 load in about 1
second rather than 9 seconds.

Change-Id: I5eb53e2a1ee853f4489e92c4ca719cfb96b4a563

gertty/db.py

@@ -24,7 +24,7 @@ import six
 import sqlalchemy
 from sqlalchemy import create_engine, MetaData, Table, Column, Integer, String, Boolean, DateTime, Text, UniqueConstraint
 from sqlalchemy.schema import ForeignKey
-from sqlalchemy.orm import mapper, sessionmaker, relationship, scoped_session
+from sqlalchemy.orm import mapper, sessionmaker, relationship, scoped_session, joinedload
 from sqlalchemy.orm.session import Session
 from sqlalchemy.sql import exists
 from sqlalchemy.sql.expression import and_
@@ -815,9 +815,12 @@ class DatabaseSession(object):
         except sqlalchemy.orm.exc.NoResultFound:
             return self.createSyncQuery(name)
 
-    def getChange(self, key):
+    def getChange(self, key, lazy=True):
+        query = self.session().query(Change).filter_by(key=key)
+        if not lazy:
+            query = query.options(joinedload(Change.revisions).joinedload(Revision.files).joinedload(File.comments))
         try:
-            return self.session().query(Change).filter_by(key=key).one()
+            return query.one()
         except sqlalchemy.orm.exc.NoResultFound:
             return None
 

gertty/view/change.py

@@ -618,7 +618,7 @@ class ChangeView(urwid.WidgetWrap):
 
     def refresh(self):
         with self.app.db.getSession() as session:
-            change = session.getChange(self.change_key)
+            change = session.getChange(self.change_key, lazy=False)
             # When we first open the change, update its last_seen
             # time.
             if not self.marked_seen: