How do you validate a GraphQL mutation in Python

Question

I am new to GraphQL. I am using Graphene-Django and have a mutation called CreateUser. It takes three arguments username, email, password.

How do I validate the data and return multiple errors back?

I want something like this returned.

{  
   "name":[  
      "Ensure this field has at least 2 characters."
   ],
   "email":[  
      "This field may not be blank."
   ],
   "password":[  
      "This field may not be blank."
   ]
}

So I can render the errors on the form like this:

My code so far:

from django.contrib.auth.models import User as UserModel
from graphene_django import DjangoObjectType
import graphene


class User(DjangoObjectType):
    class Meta:
        model = UserModel
        only_fields = 'id', 'username', 'email'


class Query(graphene.ObjectType):
    users = graphene.List(User)
    user = graphene.Field(User, id=graphene.Int())

    def resolve_users(self, info):
        return UserModel.objects.all()

    def resolve_user(self, info, **kwargs):
        try:
            return UserModel.objects.get(id=kwargs['id'])
        except (UserModel.DoesNotExist, KeyError):
            return None


class CreateUser(graphene.Mutation):

    class Arguments:
        username = graphene.String()
        email = graphene.String()
        password = graphene.String()

    user = graphene.Field(User)

    def mutate(self, info, username, email, password):
        user = UserModel.objects.create_user(username=username, email=email, password=password)
        return CreateUser(user=user)


class Mutation(graphene.ObjectType):
    create_user = CreateUser.Field()


schema = graphene.Schema(query=Query, mutation=Mutation)

Answer 1

Model errors in the schema, primarily by using unions.

In SDL format:

type RegisterUserSuccess {
  user: User!
}

type FieldError {
  fieldName: String!
  errors: [String!]!
}

type RegisterUserError {
  fieldErrors: [FieldError!]!
  nonFieldErrors: [String!]!
}


union RegisterUserPayload = RegisterUserSuccess | RegisterUserError

mutation {
  registerUser(name: String, email: String, password: String): RegisterUserPayload!
}