Make resource identifiers immutable

CHANGELOG.rst

@@ -1,6 +1,13 @@
 Changelog
 =========
 
+Next Release - (TBD)
+--------------------
+
+* bugfix:Identifier: Make resource identifiers immutable.
+  (`issue 246 <https://github.com/boto/boto3/pull/246>`__)
+
+
 1.1.3 - 2015-09-03
 ------------------
 

boto3/resources/base.py

@@ -99,7 +99,7 @@ def __init__(self, *args, **kwargs):
         # Allow setting identifiers as positional arguments in the order
         # in which they were defined in the ResourceJSON.
         for i, value in enumerate(args):
-            setattr(self, self.meta.identifiers[i], value)
+            setattr(self, '_' + self.meta.identifiers[i], value)
 
         # Allow setting identifiers via keyword arguments. Here we need
         # extra logic to ignore other keyword arguments like ``client``.
@@ -110,7 +110,7 @@ def __init__(self, *args, **kwargs):
             if name not in self.meta.identifiers:
                 raise ValueError('Unknown keyword argument: {0}'.format(name))
 
-            setattr(self, name, value)
+            setattr(self, '_' + name, value)
 
         # Validate that all identifiers have been set.
         for identifier in self.meta.identifiers:

boto3/resources/factory.py

@@ -112,7 +112,7 @@ def _load_identifiers(self, attrs, meta, model):
         """
         for identifier in model.identifiers:
             meta.identifiers.append(identifier.name)
-            attrs[identifier.name] = None
+            attrs[identifier.name] = self._create_identifier(identifier.name)
 
     def _load_actions(self, attrs, model, resource_defs, service_model):
         """
@@ -194,6 +194,23 @@ def _load_waiters(self, attrs, model):
         for waiter in model.waiters:
             attrs[waiter.name] = self._create_waiter(waiter)
 
+    def _create_identifier(factory_self, name):
+        """
+        Creates a read-only property for identifier attributes.
+        """
+        def identifier(self):
+            # The default value is set to ``None`` instead of
+            # raising an AttributeError because when resources are
+            # instantiated a check is made such that none of the
+            # identifiers have a value ``None``. If any are ``None``,
+            # a more informative user error than a generic AttributeError
+            # is raised.
+            return getattr(self, '_' + name, None)
+
+        identifier.__name__ = str(name)
+        identifier.__doc__ = 'TODO'
+        return property(identifier)
+
     def _create_autoload_property(factory_self, name, snake_cased):
         """
         Creates a new property on the resource to lazy-load its value

tests/unit/resources/test_factory.py

@@ -648,6 +648,13 @@ def test_dangling_resource_raises_for_unknown_arg(self):
         with self.assertRaises(ValueError):
             resource.Queue(url='foo', bar='baz')
 
+    def test_dangling_resource_identifier_is_immutable(self):
+        resource = self.load('test', 'test', self.model, self.defs, None)()
+        queue = resource.Queue('url')
+        # We should not be able to change the identifier's value
+        with self.assertRaises(AttributeError):
+            queue.url = 'foo'
+
     def test_dangling_resource_equality(self):
         resource = self.load('test', 'test', self.model, self.defs, None)()