Conventions for setting up a GraphQL Server on Rails - Custom types for mutations

update_post_and_type.rb

# app/graphql/mutations/update_post.rb
module Mutations
  class UpdatePost < GraphQL::Schema::Mutation
    argument :post_id, ID, required: true
    argument :description, String, required: true
  
    description "Create a new post in a team"

    field :post, Types::UpdatedPostType, null: true
    field :errors, [String], null: false

    def resolve(params)
      mutator = UpdatePostMutator.new(context, params)

      if mutator.valid?
        { post: mutator.update_post, errors: [] }
      else        
        { post: nil, errors: mutator.errors.full_messages }
      end
    end
  end
end

# app/graphql/types/update_post_type.rb
module Types
  class UpdatePostType < Types::BaseObject
    field :comments, Integer, null: false
    field :updated_at, Types::ISO8601DateTime, null: false
    field :diff, String, null: false

    def comments
      object.comments.count
    end
    
    def diff
      Posts::DiffService.new(object).last_diff
    end
  end
end