Metaprogramming when implement Rest API

restful_responsable.rb

module RestfulResponsable
  extend ActiveSupport::Concern

  included do
    # ==== Callbacks ====
    before_action :auto_set_resource, only: %i[show update destroy]
  end

  # ==== Below are 4 basic actions - CRUD of a restful api ====
  # Use metaprogramming techniques to provide all shared functions!
  def create
    instance_variable_set("@#{resource_name}", resource_class.new(resource_params))
    return error_422(resource_object.errors) unless resource_object.valid?

    resource_object.save!
    render :show, status: :created
  end

  def show
    render :show, status: :ok
  end

  def update
    resource_object.assign_attributes(resource_params)
    return error_422(resource_object.errors) unless resource_object.valid?

    resource_object.save!
    render :show, status: :ok
  end

  def destroy
    resource_object.destroy!
    head :no_content
  end

  private

  #
  # The singular name for the resource class based on the controller
  # Ex: cars_controller.rb will return "car" string
  def resource_name
    @resource_name ||= controller_name.singularize
  end

  #
  # The resource class based on the controller
  # Ex: cars_controller.rb will return "Car" class
  def resource_class
    @resource_class ||= resource_name.classify.constantize
  end

  #
  # The controller for the resource must implement method "#{resource_name}_params" to
  # limit permitted parameters for the individual model
  # Ex: cars_controller.rb will return "car_params" method
  def resource_params
    @resource_params ||= send("#{resource_name}_params")
  end

  #
  # Returns the resource from the created instance variable
  # Ex: cars_controller.rb will return "@car" instance variable
  def resource_object
    instance_variable_get("@#{resource_name}")
  end

  #
  # Use callbacks to share common setup or constraints between actions.
  #
  def auto_set_resource(resource = nil)app/controllers/concerns/restful_responsable.rb
    resource ||= resource_class.find_by!(id: params[:id])
    instance_variable_set("@#{resource_name}", resource)
  end
end