Create_update_mutation.py

class CreateBook(relay.ClientIDMutation):
  
    class Input:
        # BookCreateInput class used as argument here.
        book = graphene.Argument(BookCreateInput)

    new_book = graphene.Field(BookNode)

    @classmethod
    def mutate_and_get_payload(cls, args, context, info):

        book_data = args.get('book') # get the book input from the args
        book = Book() # get an instance of the book model here
        new_book = update_create_instance(book, book_data) # use custom function to create book

        return cls(new_book=new_book) # newly created book instance returned.


class UpdateBook(relay.ClientIDMutation):

    class Input:
        book = graphene.Argument(BookCreateInput) # get the book input from the args
        id = graphene.String(required=True) # get the book id

    errors = graphene.List(graphene.String)
    updated_book = graphene.Field(BookNode)

    @classmethod
    def mutate_and_get_payload(cls, args, context, info):

        try:
            book_instance = get_object(Book, args['id']) # get book by id
            if book_instance:
                # modify and update book model instance
                book_data = args.get('book')
                updated_book = update_create_instance(book_instance, book_data)
                return cls(updated_book=updated_book)
        except ValidationError as e:
            # return an error if something wrong happens
            return cls(updated_book=None, errors=get_errors(e))