catch validation errors during patch serialization

- we want to force triggering of validation exceptions during
serialiation
- add unit test to verify that validation exception is raised on patch
- a validation exception should be raised when a validation error occurs
during serialization
- create a serializer class that automatically throws the validation
exception
- uses marshmallow's ValidationError exception, but in theory any
exception could be used to force the check in order to pass them
through to the flask-restless validations exceptions handler and
thus have it return meaningful errors to client

fix spacing issue caught by houndci

flask_restless/views/resources.py

@@ -721,6 +721,8 @@ def patch(self, resource_id):
                 result = self.serializer.serialize(instance, only=only)
             except SerializationException as exception:
                 return errors_from_serialization_exceptions([exception])
+            except self.validation_exceptions as exception:
+                return self._handle_validation_exception(exception)
             status = 200
         else:
             result = dict()

requirements/test.txt

@@ -1,2 +1,3 @@
 -r install.txt
 unittest2
+marshmallow

tests/helpers.py

@@ -39,6 +39,7 @@
 from sqlalchemy.orm.session import Session as SessionBase
 from sqlalchemy.types import CHAR
 from sqlalchemy.types import TypeDecorator
+from marshmallow import ValidationError
 
 from flask_restless import APIManager
 from flask_restless import collection_name
@@ -119,6 +120,29 @@ def deserialize_many(self, *args, **kw):
         raise DeserializationException
 
 
+class raise_s_validation_error(DefaultSerializer):
+    """A serializer that unconditionally raises a validation error when
+    either :meth:`.serialize` or :meth:`.serialize_many` is called.
+
+    This class is useful for tests of validation errors.
+
+    """
+
+    def serialize(self, instance, *args, **kw):
+        """Immediately raises a :exc:`ValidationError` with
+        access to the provided `instance` of a SQLAlchemy model.
+
+        """
+        raise ValidationError(instance)
+
+    def serialize_many(self, instances, *args, **kw):
+        """Immediately raises a :exc:`ValidationError`.
+
+        This function requires `instances` to be non-empty.
+
+        """
+        raise ValidationError(instances[0])
+
 def isclass(obj):
     """Returns ``True`` if and only if the specified object is a type (or a
     class).

tests/test_updating.py

@@ -41,6 +41,7 @@
 from sqlalchemy.ext.hybrid import hybrid_property
 from sqlalchemy.orm import backref
 from sqlalchemy.orm import relationship
+from marshmallow import ValidationError
 
 from flask_restless import APIManager
 from flask_restless import JSONAPI_MIMETYPE
@@ -55,6 +56,7 @@
 from .helpers import MSIE9_UA
 from .helpers import ManagerTestBase
 from .helpers import raise_s_exception as raise_exception
+from .helpers import raise_s_validation_error as raise_validation_error
 
 
 class TestUpdating(ManagerTestBase):
@@ -893,6 +895,34 @@ def test_serialization_exception(self):
         check_sole_error(response, 500, ['Failed to serialize', 'type', 'tag',
                                          'ID', '1'])
 
+    def test_serialization_validation_error(self):
+        """Tests that serialization validation errors are caught when
+        responding with content.
+
+        A representation of the modified resource is returned to the
+        client when an update causes additional changes in the resource
+        in ways other than those specified by the client.
+
+        """
+        tag = self.Tag(id=1)
+        self.session.add(tag)
+        self.session.commit()
+        self.manager.create_api(self.Tag, methods=['PATCH'],
+                                validation_exceptions=[ValidationError],
+                                serializer_class=raise_validation_error)
+        data = {
+            'data': {
+                'type': 'tag',
+                'id': '1',
+                'attributes': {
+                    'name': u'foo'
+                }
+            }
+        }
+        response = self.app.patch('/api/tag/1', data=dumps(data))
+        assert response.status_code == 400
+        assert response.status == '400 BAD REQUEST'
+
     def test_dont_assign_to_method(self):
         """Tests that if a certain method is to be included in a
         resource, that method is not assigned to when updating the