Inspired by "Making ActiveRecord Thin"

gistfile1.rb

customer    = Shop::Directory.new(repository: User).find(1001)
product     = Shop::Warehouse.new(repository: Product).find(1002)
transaction = Shop::Transaction.new(customer: customer, product: product, orders: Orders.new(repository: Order))

transaction.commit

module Shop

  class Warehouse
    attr_reader :repository
    
    def initialize(args)
      @repository = args[:repository]
    end

    def find(id)
      Product.new repository.find_by_id(id)
    end
  end


  class Directory
    attr_reader :repository

    def initialize(args)
      @respository = args[:repository]
    end

    def find(id)
      Customer.new repository.find_by_id(id)
    end
  end


  class Orders
    attr_reader :repository

    def initialize(args)
      @repository = args[:repository]
    end
    
    def create(customer, product)
      Order.new repository.create(customer: customer.record, product: product.record)
    end
  end


  class Product
    attr_reader :record

    def initialize(args)
      @record = args[:record]
    end

    def sold!
      @record.update_attribute(:sold, true)
    end
  end
  

  class Customer
    attr_reader :record

    def initialize(args)
      @record = args[:record]
    end

    def pay(product)
      # perform the payment
    end
  end


  class Order
    attr_reader :record

    def initialize(args)
      @record = args[:record]
    end
  end


  class Transaction
    attr_reader :customer, :product, :orders, :status

    def initialize(args)
      @customer 	= args[:customer]
      @product  	= args[:product]
      @orders   	= args[:orders]
    end

    def commit
      @status = customer.pay(product)

      if success?
        commit!
      end
    end

    def commit!
      create_order

      if order.persisted?
        mark_product_as_sold
      end
    end

    def success?
      status === true
    end

    private

    def create_order
      @order = repository.create(customer, product)
    end

    def mark_product_as_sold
      @product.sold!
    end
  end
end