Prevent caller from specifying id during Aggregate.create()

The patch is to remove id when it was set before creating an aggregate
in objects, and check if the aggregate exists before it is created.

Related to blueprint icehouse-objects.

Change-Id: I0d7c5c5da9a93e52c7fee9eee7df80d2f460593e

nova/objects/aggregate.py

@@ -58,6 +58,9 @@ class Aggregate(base.NovaPersistentObject, base.NovaObject):
 
     @base.remotable
     def create(self, context):
+        if self.obj_attr_is_set('id'):
+            raise exception.ObjectActionError(action='create',
+                                              reason='already created')
         self._assert_no_hosts('create')
         updates = self.obj_get_changes()
         payload = dict(updates)
@@ -68,6 +71,7 @@ class Aggregate(base.NovaPersistentObject, base.NovaObject):
                                                     "create.start",
                                                     payload)
         metadata = updates.pop('metadata', None)
+        updates.pop('id', None)
         db_aggregate = db.aggregate_create(context, updates, metadata=metadata)
         self._from_db_object(context, self, db_aggregate)
         payload['aggregate_id'] = self.id

nova/tests/objects/test_aggregate.py

@@ -53,6 +53,18 @@ class _TestAggregateObject(object):
         agg.create(self.context)
         self.compare_obj(agg, fake_aggregate, subs=SUBS)
 
+    def test_recreate_fails(self):
+        self.mox.StubOutWithMock(db, 'aggregate_create')
+        db.aggregate_create(self.context, {'name': 'foo'},
+                            metadata={'one': 'two'}).AndReturn(fake_aggregate)
+        self.mox.ReplayAll()
+        agg = aggregate.Aggregate()
+        agg.name = 'foo'
+        agg.metadata = {'one': 'two'}
+        agg.create(self.context)
+        self.assertRaises(exception.ObjectActionError, agg.create,
+                          self.context)
+
     def test_save(self):
         self.mox.StubOutWithMock(db, 'aggregate_update')
         db.aggregate_update(self.context, 123, {'name': 'baz'}).AndReturn(