From 98a9c7161d1842b41f69429021bce2e50092332d Mon Sep 17 00:00:00 2001
From: Patrick Arminio <patrick.arminio@gmail.com>
Date: Sun, 28 Oct 2018 19:40:44 +0000
Subject: [PATCH] Type errors for serializer mutation

---
 graphene_django/rest_framework/mutation.py    | 25 +++++++++++++++----
 .../rest_framework/tests/test_mutation.py     | 20 ++++++++++++++-
 2 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/graphene_django/rest_framework/mutation.py b/graphene_django/rest_framework/mutation.py
index 5e343aa..0a88ec2 100644
--- a/graphene_django/rest_framework/mutation.py
+++ b/graphene_django/rest_framework/mutation.py
@@ -40,10 +40,6 @@ class SerializerMutation(ClientIDMutation):
     class Meta:
         abstract = True
 
-    errors = graphene.List(
-        ErrorType, description="May contain more than one error for same field."
-    )
-
     @classmethod
     def __init_subclass_with_meta__(
         cls,
@@ -55,7 +51,6 @@ class SerializerMutation(ClientIDMutation):
         exclude_fields=(),
         **options
     ):
-
         if not serializer_class:
             raise Exception("serializer_class is required for the SerializerMutation")
 
@@ -78,6 +73,26 @@ class SerializerMutation(ClientIDMutation):
             serializer, only_fields, exclude_fields, is_input=False
         )
 
+        error_fields = {
+            key: graphene.List(graphene.NonNull(graphene.String))
+            for key in input_fields.keys()
+        }
+
+        # TODO: from settings
+        error_fields['non_field_errors'] = graphene.List(
+            graphene.NonNull(graphene.String)
+        )
+
+        base_name = cls.__name__
+
+        cls.Errors = type(
+            "{}Errors".format(base_name),
+            (graphene.ObjectType, ),
+            yank_fields_from_attrs(error_fields, _as=Field),
+        )
+
+        output_fields['errors'] = graphene.Field(cls.Errors, required=True)
+
         _meta = SerializerMutationOptions(cls)
         _meta.lookup_field = lookup_field
         _meta.model_operations = model_operations
diff --git a/graphene_django/rest_framework/tests/test_mutation.py b/graphene_django/rest_framework/tests/test_mutation.py
index 4dccc18..5afe3cc 100644
--- a/graphene_django/rest_framework/tests/test_mutation.py
+++ b/graphene_django/rest_framework/tests/test_mutation.py
@@ -1,6 +1,6 @@
 import datetime
 
-from graphene import Field, ResolveInfo
+from graphene import Field, ResolveInfo, NonNull, List, String
 from graphene.types.inputobjecttype import InputObjectType
 from py.test import raises
 from py.test import mark
@@ -177,3 +177,21 @@ def test_invalid_serializer_operations():
                 model_operations = ["Add"]
 
     assert "model_operations" in str(exc.value)
+
+
+def test_errors_field():
+    class MyMutation(SerializerMutation):
+        class Meta:
+            serializer_class = MySerializer
+
+    errors_field = MyMutation._meta.fields['errors']
+
+    assert MyMutation.Errors
+
+    assert type(errors_field.type) == NonNull
+
+    errors_field = errors_field.type.of_type
+
+    assert type(errors_field.model.type) == List
+    assert type(errors_field.model.type.of_type) == NonNull
+    # TODO: how to test that the nonnull type is a string?