# app/models/graph/post_type.rb
module Graph
  PostType = GraphQL::ObjectType.define do
    name "Post"
    description "A post"

    field :id, types.ID
    field :name, types.String
  end
end

# app/models/graph/query_type.rb
module Graph
  QueryType = GraphQL::ObjectType.define do
    name "Query"
    description "The query root of this schema"

    field :post, PostType do
      argument :id, !types.ID, "The ID of the post"
      resolve -> (_object, arguments, _context) do
        Post.find(arguments[:id])
      end
    end
  end
end

# app/models/graph/mutation_type.rb
module Graph
  MutationType = GraphQL::ObjectType.define do
    name "Mutation"
    description "Mutations"

    field :postCreate, PostType do
      argument :name, !types.String, "The post name"
      resolve -> (_object, arguments, _context) do
        Post.create(name: arguments[:name])
      end
    end
  end
end

# app/models/graph/schema.rb
module Graph
  Schema = GraphQL::Schema.define do
    query Graph::QueryType
    mutation Graph::MutationType
  end
end

# app/controllers/graph_controller.rb
class GraphController < ApplicationController
  def execute
    render json: ::Graph::Schema.execute(
      params.fetch("query"),
      context: {} # you can pass the current_user here
    )
  end
end

# config/routes.rb
get 'graph', to: 'graph#execute'