Fix asymmetric view of object fields

This adds an obj_fields property which returns a combined view of the
real field key names as well as the extra_fields. This will help
avoid bugs where we forget to consider extra_fields.

Change-Id: I93351ccc9f87817deca06e9a2d94f82a3dd5f51a
Closes-bug: 1223888

nova/objects/base.py

@@ -341,20 +341,23 @@ class NovaObject(object):
         False if not. Raises AttributeError if attrname is not
         a valid attribute for this object.
         """
-        if (attrname not in self.fields and
-                attrname not in self.obj_extra_fields):
+        if attrname not in self.obj_fields:
             raise AttributeError(
                 _("%(objname)s object has no attribute '%(attrname)s'") %
                 {'objname': self.obj_name(), 'attrname': attrname})
         return hasattr(self, get_attrname(attrname))
 
+    @property
+    def obj_fields(self):
+        return self.fields.keys() + self.obj_extra_fields
+
     # dictish syntactic sugar
     def iteritems(self):
         """For backwards-compatibility with dict-based objects.
 
         NOTE(danms): May be removed in the future.
         """
-        for name in self.fields.keys() + self.obj_extra_fields:
+        for name in self.obj_fields:
             if (self.obj_attr_is_set(name) or
                     name in self.obj_extra_fields):
                 yield name, getattr(self, name)
@@ -390,7 +393,7 @@ class NovaObject(object):
 
         NOTE(danms): May be removed in the future.
         """
-        if key not in self.fields:
+        if key not in self.obj_fields:
             raise AttributeError("'%s' object has no attribute '%s'" % (
                     self.__class__, key))
         if value != NotSpecifiedSentinel and not self.obj_attr_is_set(key):

nova/tests/objects/test_objects.py

@@ -599,6 +599,18 @@ class _TestObject(object):
         obj.obj_reset_changes()
         self.assertEqual({}, obj.obj_get_changes())
 
+    def test_obj_fields(self):
+        class TestObj(base.NovaObject):
+            fields = {'foo': int}
+            obj_extra_fields = ['bar']
+
+            @property
+            def bar(self):
+                return 'this is bar'
+
+        obj = TestObj()
+        self.assertEqual(['foo', 'bar'], obj.obj_fields)
+
 
 class TestObject(_LocalTest, _TestObject):
     pass