Wrap or not wrap. Root is the question

graphene/contrib/django/tests/test_types.py

@@ -1,3 +1,4 @@
+from pytest import raises
 from graphql.core.type import GraphQLInterfaceType, GraphQLObjectType
 from mock import patch
 
@@ -33,10 +34,11 @@ def test_django_interface():
     assert DjangoNode._meta.is_interface is True
 
 
-@patch('graphene.contrib.django.tests.models.Article.objects.filter')
-def test_django_get_node(objects):
-    Human.get_node(1)
-    objects.assert_called_with(id=1)
+@patch('graphene.contrib.django.tests.models.Article.objects.get', return_value=Article(id=1))
+def test_django_get_node(get):
+    human = Human.get_node(1)
+    get.assert_called_with(id=1)
+    assert human.id == 1
 
 
 def test_pseudo_interface_registered():
@@ -67,10 +69,26 @@ def test_node_replacedfield():
 
 
 def test_interface_resolve_type():
-    resolve_type = Character.resolve_type(schema, Human(object()))
+    resolve_type = Character.resolve_type(schema, Human())
     assert isinstance(resolve_type, GraphQLObjectType)
 
 
+def test_interface_objecttype_init_none():
+    h = Human()
+    assert h._root is None
+
+
+def test_interface_objecttype_init_good():
+    instance = Article()
+    h = Human(instance)
+    assert h._root == instance
+
+
+def test_interface_objecttype_init_unexpected():
+    with raises(AssertionError) as excinfo:
+        Human(object())
+    assert str(excinfo.value) == "Human received a non-compatible instance (object) when expecting Article"
+
 def test_object_type():
     object_type = schema.T(Human)
     Human._meta.fields_map

graphene/contrib/django/types.py

@@ -38,12 +38,19 @@ class DjangoObjectTypeMeta(ObjectTypeMeta):
 
 class InstanceObjectType(BaseObjectType):
 
-    def __init__(self, instance=None):
-        self.instance = instance
-        super(InstanceObjectType, self).__init__()
+    def __init__(self, _root=None):
+        if _root:
+            assert isinstance(_root, self._meta.model), (
+                '{} received a non-compatible instance ({}) '
+                'when expecting {}'.format(
+                    self.__class__.__name__,
+                    _root.__class__.__name__,
+                    self._meta.model.__name__
+                ))
+        super(InstanceObjectType, self).__init__(_root=_root)
 
     def __getattr__(self, attr):
-        return getattr(self.instance, attr)
+        return getattr(self._root, attr)
 
 
 class DjangoObjectType(six.with_metaclass(
@@ -61,5 +68,8 @@ class DjangoNode(BaseNode, DjangoInterface):
 
     @classmethod
     def get_node(cls, id):
-        instance = cls._meta.model.objects.filter(id=id).first()
-        return cls(instance)
+        try:
+            instance = cls._meta.model.objects.get(id=id)
+            return cls(instance)
+        except cls._meta.model.DoesNotExist:
+            return None

graphene/core/schema.py

@@ -113,7 +113,7 @@ class Schema(object):
         return self.executor.execute(
             self.schema,
             request,
-            root=self.query(root),
+            root=root,
             args=vars,
             operation_name=operation_name,
             **kwargs

graphene/core/types/field.py

@@ -1,4 +1,5 @@
 from collections import OrderedDict
+from functools import wraps
 
 import six
 from graphql.core.type import GraphQLField, GraphQLInputObjectField
@@ -76,6 +77,14 @@ class Field(OrderedType):
             assert len(arguments) == 0
             arguments = type_objecttype.get_arguments()
             resolver = getattr(type_objecttype, 'mutate')
+        else:
+            my_resolver = resolver
+            @wraps(my_resolver)
+            def wrapped_func(instance, args, info):
+                if not isinstance(instance, self.object_type):
+                    instance = self.object_type(_root=instance)
+                return my_resolver(instance, args, info)
+            resolver = wrapped_func
 
         resolver = snake_case_args(resolver)
         assert type, 'Internal type for field %s is None' % str(self)

graphene/core/types/objecttype.py

@@ -144,6 +144,7 @@ class BaseObjectType(BaseType):
 
     def __init__(self, *args, **kwargs):
         signals.pre_init.send(self.__class__, args=args, kwargs=kwargs)
+        self._root = kwargs.pop('_root', None)
         args_len = len(args)
         fields = self._meta.fields
         if args_len > len(fields):