DCI example

money_transfer.rb

class Account < ActiveRecord::Base
  def transfer_to(destination, amount)
    self.balance -= amount
    destination.balance += amount
    destination.save
    self.save
  end
end

class TransfersController < ApplicationController
  def transfer
    @source = Account.find(params[:account_id])
    @destination = Account.find(params[:destination_id])
    
    if @source.transfer_to(@destination, params[:amount])
      flash[:success] = "Transfer successful!"
      redirect_to @source
    else
      flash[:error] = "There was a problem."
      render :transfer
    end
  end
end

class MoneyTransfer
  def initialize(source, destination)
    @source = source.extend Transferrer
    @destination = destination
  end
  
  def execute(amount)
    @source.transfer_to(@destination, amount)
  end
  
  private
  
  module Transferrer
    def transfer_to(destination, amount)
      self.balance -= amount
      destination.balance += amount
      destination.save
      self.save
    end
  end
end

class TransfersController < ApplicationController
  def transfer
    source = Account.find(params[:account_id])
    destination = Account.find(params[:destination_id])
    
    if MoneyTransfer.new(params[:account_id], params[:destination_id], self).execute(params[:amount])
      flash[:success] = "Transfer successful!"
      redirect_to source
    else
      flash[:error] = "There was a problem."
      render :transfer
    end
  end
end

class MoneyTransfer
  def initialize(source_id, destination_id, controller)
    @source = find_account(source_id).extend Transferrer
    @destination = find_account(destination_id)
    @listener = controller
  end
  
  def execute(amount)
    @source.transfer_to(
                        @destination
                        amount.to_i,
                        success: -> { @controller.go_to @source },
                        failure: -> { @controller.display_error @source}
                       )
    @source
  end
  
  private
  
  def find_account(id)
    Account.find(id)
  end
  
  module Transferrer
    def transfer_to(destination, amount, callbacks)
      transaction do
        self.balance -= amount
        destination.balance += amount
        destination.save
        self.save
        callbacks[:success].call
      rescue => e
        callbacks[:failure].call
      end
    end
  end
end

class TransfersController < ApplicationController
  def transfer
    MoneyTransfer.new(params[:account_id], params[:destination_id], self).execute(params[:amount])
  end
  
  private
  
  def go_to(resource_or_action)
    case resource_or_action
    when Symbol
      render resource_or_action
    else
      redirect_to resource_or_action
    end
  end
end