Add instance_group_get_by_instance to db.api

Add a new method to the db.api that lets you get an instance group by
instance UUID.

Change-Id: I3d2a019c8f97166ec55574c610d12f572afb2bd1
Related-bug: #1379451

nova/db/api.py

@@ -781,6 +781,11 @@ def instance_group_get(context, group_uuid):
     return IMPL.instance_group_get(context, group_uuid)
 
 
+def instance_group_get_by_instance(context, instance_uuid):
+    """Get the group an instance is a member of."""
+    return IMPL.instance_group_get_by_instance(context, instance_uuid)
+
+
 def instance_group_update(context, group_uuid, values):
     """Update the attributes of an group."""
     return IMPL.instance_group_update(context, group_uuid, values)

nova/db/sqlalchemy/api.py

@@ -5932,6 +5932,25 @@ def instance_group_get(context, group_uuid):
     return group
 
 
+def instance_group_get_by_instance(context, instance_uuid):
+    session = get_session()
+    with session.begin():
+        group_member = model_query(context, models.InstanceGroupMember,
+                                   session=session).\
+                                   filter_by(instance_id=instance_uuid).\
+                                   first()
+        if not group_member:
+            raise exception.InstanceGroupNotFound(group_uuid='')
+        group = _instance_group_get_query(context, models.InstanceGroup,
+                                          models.InstanceGroup.id,
+                                          group_member.group_id,
+                                          session=session).first()
+        if not group:
+            raise exception.InstanceGroupNotFound(
+                    group_uuid=group_member.group_id)
+        return group
+
+
 def instance_group_update(context, group_uuid, values):
     """Update the attributes of an group.
 

nova/tests/db/test_db_api.py

@@ -7092,6 +7092,18 @@ class InstanceGroupDBApiTestCase(test.TestCase, ModelsObjectComparatorMixin):
                           db.instance_group_update, self.context,
                           'invalid_id', values)
 
+    def test_instance_group_get_by_instance(self):
+        values = self._get_default_values()
+        group1 = self._create_instance_group(self.context, values)
+
+        members = ['instance_id1', 'instance_id2']
+        db.instance_group_members_add(self.context, group1.uuid, members)
+
+        group2 = db.instance_group_get_by_instance(self.context,
+                                                   'instance_id1')
+
+        self.assertEqual(group2.uuid, group1.uuid)
+
 
 class InstanceGroupMembersDBApiTestCase(InstanceGroupDBApiTestCase):
     def test_instance_group_members_on_create(self):