From a79df01449f00bc44fe2c78d1d8a9f6ce440625f Mon Sep 17 00:00:00 2001
From: Greg Back <gback@mitre.org>
Date: Fri, 24 Feb 2017 13:07:54 -0600
Subject: [PATCH] Convert more fields to Property classes.

---
 stix2/base.py                        | 27 +++++++++++----------------
 stix2/bundle.py                      |  2 +-
 stix2/common.py                      | 12 ++++++------
 stix2/test/test_kill_chain_phases.py |  2 +-
 4 files changed, 19 insertions(+), 24 deletions(-)

diff --git a/stix2/base.py b/stix2/base.py
index 4d1572e..4121570 100644
--- a/stix2/base.py
+++ b/stix2/base.py
@@ -65,27 +65,22 @@ class _STIXBase(collections.Mapping):
                                                prop_metadata.get('default', lambda x: ''))(cls),
                 )
                 raise ValueError(msg)
-        elif prop_metadata.get('fixed'):
-            if kwargs[prop_name] != prop_metadata['fixed']:
-                msg = prop_metadata.get('error_msg', DEFAULT_ERROR).format(
-                    type=class_name,
-                    field=prop_name,
-                    expected=prop_metadata['fixed']
-                )
-                raise ValueError(msg)
 
     def _check_property(self, prop_name, prop, kwargs):
         if prop_name not in kwargs:
-            kwargs[prop_name] = prop.default()
+            if hasattr(prop, 'default'):
+                kwargs[prop_name] = prop.default()
             # if default == NOW:
             #     kwargs[prop_name] = self.__now
-        try:
-            kwargs[prop_name] = prop.validate(kwargs[prop_name])
-        except ValueError as exc:
-            msg = "Invalid value for {0} '{1}': {2}"
-            raise ValueError(msg.format(self.__class__.__name__,
-                                        prop_name,
-                                        exc))
+
+        if prop_name in kwargs:
+            try:
+                kwargs[prop_name] = prop.validate(kwargs[prop_name])
+            except ValueError as exc:
+                msg = "Invalid value for {0} '{1}': {2}"
+                raise ValueError(msg.format(self.__class__.__name__,
+                                            prop_name,
+                                            exc))
 
     def __init__(self, **kwargs):
         cls = self.__class__
diff --git a/stix2/bundle.py b/stix2/bundle.py
index 9ef71be..5785d43 100644
--- a/stix2/bundle.py
+++ b/stix2/bundle.py
@@ -11,7 +11,7 @@ class Bundle(_STIXBase):
         'type': TypeProperty(_type),
         'id': IDProperty(_type),
         'spec_version': Property(fixed="2.0"),
-        'objects': {},
+        'objects': Property(),
     }
 
     def __init__(self, *args, **kwargs):
diff --git a/stix2/common.py b/stix2/common.py
index be417af..b28e342 100644
--- a/stix2/common.py
+++ b/stix2/common.py
@@ -1,7 +1,9 @@
 """STIX 2 Common Data Types and Properties"""
 
 import re
+
 from .base import _STIXBase
+from .properties import Property
 from .utils import NOW
 
 ref_regex = ("^[a-z][a-z-]+[a-z]--[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}"
@@ -33,12 +35,10 @@ COMMON_PROPERTIES = {
 
 class ExternalReference(_STIXBase):
     _properties = {
-        'source_name': {
-            'required': True,
-        },
-        'description': {},
-        'url': {},
-        'external_id': {},
+        'source_name': Property(required=True),
+        'description': Property(),
+        'url': Property(),
+        'external_id': Property(),
     }
 
 
diff --git a/stix2/test/test_kill_chain_phases.py b/stix2/test/test_kill_chain_phases.py
index 425c4b2..f646f0a 100644
--- a/stix2/test/test_kill_chain_phases.py
+++ b/stix2/test/test_kill_chain_phases.py
@@ -25,7 +25,7 @@ FOO_PRE_ATTACK = """{
 }"""
 
 
-def test_lockheed_martin_cyber_kill_chain():
+def test_kill_chain_example():
     preattack = stix2.KillChainPhase(
         kill_chain_name="foo",
         phase_name="pre-attack",