A nicer calling convention for object instantiation

This patch makes the base object constructor take some arguments
to streamline the process of creating a new object. By taking
a context and an optional set of keyword args, we can reduce
the lines of code required to create an object from many to, often,
one.

Change-Id: Id85c70d04af500ece48e9c93ee55a8e3d579299d

nova/objects/base.py

@@ -177,9 +177,11 @@ class NovaObject(object):
     fields = {}
     obj_extra_fields = []
 
-    def __init__(self):
+    def __init__(self, context=None, **kwargs):
         self._changed_fields = set()
-        self._context = None
+        self._context = context
+        for key in kwargs.keys():
+            self[key] = kwargs[key]
 
     @classmethod
     def obj_name(cls):

nova/objects/instance.py

@@ -163,15 +163,18 @@ class Instance(base.NovaPersistentObject, base.NovaObject):
 
     def __init__(self, *args, **kwargs):
         super(Instance, self).__init__(*args, **kwargs)
-        self.obj_reset_changes()
+        self._reset_metadata_tracking()
 
-    def obj_reset_changes(self, fields=None):
-        super(Instance, self).obj_reset_changes(fields)
+    def _reset_metadata_tracking(self):
         self._orig_system_metadata = (dict(self.system_metadata) if
                                       'system_metadata' in self else {})
         self._orig_metadata = (dict(self.metadata) if
                                'metadata' in self else {})
 
+    def obj_reset_changes(self, fields=None):
+        super(Instance, self).obj_reset_changes(fields)
+        self._reset_metadata_tracking()
+
     def obj_what_changed(self):
         changes = super(Instance, self).obj_what_changed()
         if 'metadata' in self and self.metadata != self._orig_metadata:

nova/tests/objects/test_objects.py

@@ -647,6 +647,12 @@ class _TestObject(object):
         obj = TestObj()
         self.assertEqual(['foo', 'bar'], obj.obj_fields)
 
+    def test_obj_constructor(self):
+        obj = MyObj(context=self.context, foo=123, bar='abc')
+        self.assertEqual(123, obj.foo)
+        self.assertEqual('abc', obj.bar)
+        self.assertEqual(set(['foo', 'bar']), obj.obj_what_changed())
+
 
 class TestObject(_LocalTest, _TestObject):
     pass