Rails Controller Example with Command Object

1_widget_controller.rb

class WidgetController < ApplicationController
  def new
    # ...
  end
  
  def create
    AddWidgetToInventory.call(widget_params) do |on|
      on.success do |widget|
        redirect widget_path(widget), flash: "Successfully created widget"
      end
      on.failure do |widget|
        @widget = widget
        render "widgets/new"
      end
    end
  end
end

2_add_widget_to_inventory.rb

class AddWidgetToInventory
  def self.call(params, &block)
    new(params, &block).call
  end
  
  def initialize(params, &block)
    @params = params
    @handlers = ProcHash[block]
  end
  
  def call
    widget = Widget.new
    # complicated business logic
    # if something fails:
    handlers.respond_with(:failure, widget)
    
    # everything is ok
    handlers.respond_with(:success, widget)
  end
end

3_proc_hash.rb

  class ProcHash
    def self.[](block)
      self.new.tap { |proxy| block.call(proxy) }
    end

    def respond_with(callback, *args)
      callbacks[callback].call(*args)
    end

    def method_missing(method, *args, &block)
      block ? callbacks[method] = block : super
      self
    end

    private

    def callbacks
      @callbacks ||= {}
    end
  end