Add unique_key_packed to UniqueKey mixin

This allows client libraries to get a binary representation of the
unique_key.

Change-Id: Ia8523286c74b2545b72bab7448f138105ac34c83

dragonflow/db/models/mixins.py

@@ -9,6 +9,8 @@
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
 #    under the License.
+import struct
+
 from jsonmodels import fields
 
 import dragonflow.db.model_framework as mf
@@ -57,3 +59,10 @@ class UniqueKey(mf.MixinBase):
         from dragonflow.db import api_nb
         nb_api = api_nb.NbApi.get_instance()
         self.unique_key = nb_api.driver.allocate_unique_key(self.table_name)
+
+    @property
+    def unique_key_packed(self):
+        unique_key = self.unique_key
+        if unique_key is None:
+            return None
+        return struct.pack('!I', self.unique_key)

dragonflow/tests/unit/test_unique_key_mixin.py

@@ -0,0 +1,56 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import six
+
+from dragonflow import conf as cfg
+from dragonflow.db import api_nb
+from dragonflow.db import model_framework as mf
+from dragonflow.db.models import mixins
+from dragonflow.tests import base as tests_base
+
+
+@mf.register_model
+@mf.construct_nb_db_model
+class ModelWithUniqueKey(mf.ModelBase, mixins.BasicEvents, mixins.UniqueKey):
+    table_name = 'model_with_unique_key1'
+
+
+def _bytes(*args):
+    """
+    Returns a byte array (bytes in py3, str in py2) of chr(b) for
+    each b in args
+    """
+    if six.PY2:
+        return "".join(chr(c) for c in args)
+    # else: Python 3
+    return bytes(args)
+
+
+class TestUniqueKeyMixin(tests_base.BaseTestCase):
+    def setUp(self):
+        cfg.CONF.set_override('nb_db_class', '_dummy_nb_db_driver', group='df')
+        super(TestUniqueKeyMixin, self).setUp()
+
+    def test_allocate_unique_id(self):
+        nb_api = api_nb.NbApi.get_instance()
+        instance1 = ModelWithUniqueKey(id='instance1')
+        nb_api.create(instance1)
+        self.assertIsNotNone(instance1.unique_key)
+
+    def test_unique_id_packed(self):
+        instance = ModelWithUniqueKey(id='instance', unique_key=13)
+        self.assertEqual(_bytes(0, 0, 0, 13),
+                         instance.unique_key_packed)
+        instance.unique_key = 0x12345678
+        self.assertEqual(_bytes(0x12, 0x34, 0x56, 0x78),
+                         instance.unique_key_packed)