use to_representation in favor of get_attribute (#848)

* use `to_represenation` in favor of `get_attribute`

* fix datetime type does get converted to a string

to_representation will convert the datetime field into a string representation. However the to_representation on the method field will only call its underlying method.

* fix add missing import

* apply black formatter

* add test for serializer method field

* apply black format

* improve backward compatibility

by using date's class contructor instead of fromisostring

* apply black format

* fix black format issue

graphene_django/rest_framework/models.py

@@ -9,3 +9,8 @@ class MyFakeModel(models.Model):
 class MyFakeModelWithPassword(models.Model):
     cool_name = models.CharField(max_length=50)
     password = models.CharField(max_length=50)
+
+
+class MyFakeModelWithDate(models.Model):
+    cool_name = models.CharField(max_length=50)
+    last_edited = models.DateField()

graphene_django/rest_framework/mutation.py

@@ -1,6 +1,7 @@
 from collections import OrderedDict
 
 from django.shortcuts import get_object_or_404
+from rest_framework import serializers
 
 import graphene
 from graphene.relay.mutation import ClientIDMutation
@@ -158,6 +159,9 @@ class SerializerMutation(ClientIDMutation):
         kwargs = {}
         for f, field in serializer.fields.items():
             if not field.write_only:
+                if isinstance(field, serializers.SerializerMethodField):
+                    kwargs[f] = field.to_representation(obj)
+                else:
                     kwargs[f] = field.get_attribute(obj)
 
         return cls(errors=None, **kwargs)

graphene_django/rest_framework/tests/test_mutation.py

@@ -8,7 +8,7 @@ from graphene.types.inputobjecttype import InputObjectType
 
 from ...settings import graphene_settings
 from ...types import DjangoObjectType
-from ..models import MyFakeModel, MyFakeModelWithPassword
+from ..models import MyFakeModel, MyFakeModelWithPassword, MyFakeModelWithDate
 from ..mutation import SerializerMutation
 
 
@@ -33,6 +33,18 @@ class MyModelSerializer(serializers.ModelSerializer):
         fields = "__all__"
 
 
+class MyModelSerializerWithMethod(serializers.ModelSerializer):
+    days_since_last_edit = serializers.SerializerMethodField()
+
+    class Meta:
+        model = MyFakeModelWithDate
+        fields = "__all__"
+
+    def get_days_since_last_edit(self, obj):
+        now = datetime.date(2020, 1, 8)
+        return (now - obj.last_edited).days
+
+
 class MyModelMutation(SerializerMutation):
     class Meta:
         serializer_class = MyModelSerializer
@@ -208,6 +220,23 @@ def test_model_invalid_update_mutate_and_get_payload_success():
     assert '"id" required' in str(exc.value)
 
 
+@mark.django_db
+def test_perform_mutate_success():
+    class MyMethodMutation(SerializerMutation):
+        class Meta:
+            serializer_class = MyModelSerializerWithMethod
+
+    result = MyMethodMutation.mutate_and_get_payload(
+        None,
+        mock_info(),
+        **{"cool_name": "Narf", "last_edited": datetime.date(2020, 1, 4)}
+    )
+
+    assert result.errors is None
+    assert result.cool_name == "Narf"
+    assert result.days_since_last_edit == 4
+
+
 def test_mutate_and_get_payload_error():
     class MyMutation(SerializerMutation):
         class Meta: