Adding lazy loading property for dataset ID in Environment.

gcloud/datastore/_implicit_environ.py

@@ -32,14 +32,31 @@
 _DATASET_ENV_VAR_NAME = 'GCLOUD_DATASET_ID'
 
 
+class _DatasetIDProperty(object):
+    """Descriptor for lazy loaded dataset ID."""
+
+    def __get__(self, obj, objtype):
+        if obj is None or objtype is not Environment:
+            return self
+
+        obj.dataset_id = get_default_dataset_id()
+        return obj.dataset_id
+
+
 class Environment(object):
-    """Container for environment settings."""
+    """Container for environment settings.
+
+    :type dataset_id: string
+    :param dataset_id: Persistent implied dataset ID from environment.
+
+    :type connection: :class:`gcloud.datastore.connection.Connection`
+    :param connection: Persistent implied connection from environment.
+    """
 
-    dataset_id = None
-    """Attribute to allow persistent implied dataset ID from environment."""
+    dataset_id = _DatasetIDProperty()
 
-    connection = None
-    """Attribute to allow persistent implied connection from environment."""
+    def __init__(self):
+        self.connection = None
 
 
 def app_engine_id():

gcloud/datastore/test__implicit_environ.py

@@ -213,6 +213,56 @@ def test_set_implicit_three_env_appengine_and_compute(self):
         self.assertEqual(connection.timeout, None)
 
 
+class Test_lazy_loaded_dataset_id(unittest2.TestCase):
+
+    def setUp(self):
+        from gcloud.datastore import _implicit_environ
+        self._replaced_default = _implicit_environ.DEFAULT_ENVIRON
+        _implicit_environ.DEFAULT_ENVIRON = _implicit_environ.Environment()
+
+    def tearDown(self):
+        from gcloud.datastore import _implicit_environ
+        _implicit_environ.DEFAULT_ENVIRON = self._replaced_default
+
+    def test_prop_default(self):
+        from gcloud.datastore import _implicit_environ
+        from gcloud.datastore._implicit_environ import Environment
+
+        self.assertTrue(isinstance(Environment.dataset_id,
+                                   _implicit_environ._DatasetIDProperty))
+        self.assertEqual(_implicit_environ.DEFAULT_ENVIRON.dataset_id, None)
+
+    def test_prop_on_wrong_class(self):
+        from gcloud.datastore import _implicit_environ
+
+        data_prop = _implicit_environ._DatasetIDProperty()
+
+        class FakeEnv(object):
+            dataset_id = data_prop
+
+        self.assertTrue(FakeEnv.dataset_id is data_prop)
+        self.assertTrue(FakeEnv().dataset_id is data_prop)
+
+    def test_prop_descriptor(self):
+        from gcloud._testing import _Monkey
+        from gcloud.datastore import _implicit_environ
+
+        self.assertFalse(
+            'dataset_id' in _implicit_environ.DEFAULT_ENVIRON.__dict__)
+
+        DEFAULT = object()
+
+        def mock_default():
+            return DEFAULT
+
+        with _Monkey(_implicit_environ, get_default_dataset_id=mock_default):
+            lazy_loaded = _implicit_environ.DEFAULT_ENVIRON.dataset_id
+
+        self.assertEqual(lazy_loaded, DEFAULT)
+        self.assertTrue(
+            'dataset_id' in _implicit_environ.DEFAULT_ENVIRON.__dict__)
+
+
 class _AppIdentity(object):
 
     def __init__(self, app_id):