Merge "Add specific lazy-load method for instance.tags"

nova/objects/instance.py

@@ -882,6 +882,10 @@ class Instance(base.NovaPersistentObject, base.NovaObject,
                 jsonutils.loads(db_keypairs))
             self.obj_reset_changes(['keypairs'])
 
+    def _load_tags(self):
+        self.tags = objects.TagList.get_by_resource_id(
+            self._context, self.uuid)
+
     def apply_migration_context(self):
         if self.migration_context:
             self._set_migration_context_to_instance(prefix='new_')
@@ -980,11 +984,14 @@ class Instance(base.NovaPersistentObject, base.NovaObject,
             # filters on instances.deleted == 0, so if the instance is deleted
             # don't attempt to even load services since we'll fail.
             self.services = objects.ServiceList(self._context)
-        elif attrname == 'tags' and self.deleted:
-            # NOTE(mriedem): Same story as services, the DB API query
-            # in instance_tag_get_by_instance_uuid will fail if the instance
-            # has been deleted so just return an empty tag list here.
-            self.tags = objects.TagList(self._context)
+        elif attrname == 'tags':
+            if self.deleted:
+                # NOTE(mriedem): Same story as services, the DB API query
+                # in instance_tag_get_by_instance_uuid will fail if the
+                # instance has been deleted so just return an empty tag list.
+                self.tags = objects.TagList(self._context)
+            else:
+                self._load_tags()
         else:
             # FIXME(comstud): This should be optimized to only load the attr.
             self._load_generic(attrname)

nova/tests/unit/objects/test_instance.py

@@ -215,6 +215,17 @@ class _TestInstanceObject(object):
                                     deleted=True)
         self.assertEqual(0, len(instance.tags))
 
+    def test_lazy_load_tags(self):
+        instance = objects.Instance(self.context, uuid=uuids.instance,
+                                    user_id=self.context.user_id,
+                                    project_id=self.context.project_id)
+        instance.create()
+        tag = objects.Tag(self.context, resource_id=instance.uuid, tag='foo')
+        tag.create()
+        self.assertNotIn('tags', instance)
+        self.assertEqual(1, len(instance.tags))
+        self.assertEqual('foo', instance.tags[0].tag)
+
     @mock.patch.object(db, 'instance_get')
     def test_get_by_id(self, mock_get):
         mock_get.return_value = self.fake_instance