Ignore unknown attributes during MapAttribute deserialization. Fixes pynamodb#358 (pynamodb#359)

mathewmarcus · jpinner-lyft · commit 14e2507cef68 · 2017-11-08T13:27:41.000-06:00
diff --git a/docs/attributes.rst b/docs/attributes.rst
@@ -192,3 +192,5 @@ These attributes can then be used inside of Model classes just like any other at
     class CarInfoMap(MapAttribute):
         make = UnicodeAttribute(null=False)
         model = UnicodeAttribute(null=True)
+
+`As with a model and its top-level attributes <https://github.com/pynamodb/PynamoDB/blob/master/docs/quickstart.rst#changing-items>`_, a PynamoDB MapAttribute will ignore sub-attributes it does not know about during deserialization. As a result, if the item in DynamoDB contains sub-attributes not declared as properties of the corresponding MapAttribute, save() will cause those sub-attributes to be deleted.
diff --git a/pynamodb/attributes.py b/pynamodb/attributes.py
@@ -765,6 +765,8 @@ def deserialize(self, values):
             attr_value = _get_value_for_deserialize(v)
             key = self._dynamo_to_python_attr(k)
             attr_class = self._get_deserialize_class(key, v)
+            if attr_class is None:
+                continue
             deserialized_value = None
             if attr_value is not None:
                 deserialized_value = attr_class.deserialize(attr_value)
diff --git a/pynamodb/tests/test_attributes.py b/pynamodb/tests/test_attributes.py
@@ -603,6 +603,23 @@ def test_map_overridden_attrs_serialize(self):
         expected = {'number_attr': {'N': '10'}, 'unicode_attr': {'S': six.u('Hello')}}
         assert CustomAttrMap().serialize(attribute) == expected
 
+    def test_additional_attrs_deserialize(self):
+        raw_data = {
+            'number_attr': {
+                'N': '10'},
+            'unicode_attr': {
+                'S': six.u('Hello')
+            },
+            'undeclared_attr': {
+                'S': six.u('Goodbye')
+            }
+        }
+        expected = {
+            'overridden_number_attr': 10,
+            'overridden_unicode_attr': "Hello"
+        }
+        assert CustomAttrMap().deserialize(raw_data).attribute_values == expected
+
     def test_defaults(self):
         item = DefaultsMap()
         assert item.validate()
