can't write unknown attribute `client_mutation_id`

Question

I'm trying to write my first mutation in Graphql with RoR. It seems like this:

app/graphql/mutations/create_post.rb

module Mutations
    class CreatePost < Mutations::BaseMutation
        argument :title, String, required: true
        argument :body, String, required: true

        type Types::PostType

        def resolve(title: nil, body: nil)
            Post.create!(title: title, body: body)
        end
    end
end

But every time I make request using Graphiql (like this:)

mutation createPost {
  createPost(input:{
    title:"dupa",
    body:"dupa"
  }) {
    id
  }
}

The post gets saved in database, but I recive an error

"error": {
    "message": "can't write unknown attribute `client_mutation_id`" [...]

instead of requested id How can I solve this problem? this is my

app/graphql/mutations/base_mutation.rb

module Mutations
    class BaseMutation < GraphQL::Schema::RelayClassicMutation
    end
end

app/graphql/types/mutation_type.rb

module Types
  class MutationType < Types::BaseObject
    field :create_post, mutation: Mutations::CreatePost
  end
end

github link if it can help: https://github.com/giraffecms/GiraffeCMS-backend-rails/tree/blog/app/graphql

Answer 1

The Relay Input Object Mutations Specification lays down some requirements on what mutation inputs and outputs look like, and graphql-ruby can generate some of this boilerplate for you. In particular, you don't directly specify the type of the mutation response; graphql-ruby generates a "payload" type for you, and you have to specify the fields that go into it.

That is, I think it should work to say:

class Mutations::CreatePost < Mutations::BaseMutation
    argument :title, String, required: true
    argument :body, String, required: true

    field :post, Types::PostType, null: false

    def resolve(title: nil, body: nil)
        post = Post.create!(title: title, body: body)
        { post: post }
    end
end

The API docs note (emphasis from original):

An argument called clientMutationId is always added, but it’s not passed to the resolve method. The value is re-inserted to the response. (It’s for client libraries to manage optimistic updates.)

So when your original version tries to return the model object directly, graphql-ruby tries to set #client_mutation_id on it, and that results in the error you're getting.