Notes/sample code from CPH.rb http://lanyrd.com/2013/copenhagen-ruby-brigade-october/scpmwy/

0-notes.md

Pub-Sub patterns for better OO code

• it's not new; it's just event-driven programming
• GoF observer pattern

I thought of objects being like biological cells and/or individual computers on a network, only able to communicate with messages (so messaging came at the very beginning -- it took a while to see how to do messaging in a programming language efficiently enough to be useful) - Allen Kay

Recent articles/videos

• the real meaning of "tell don't ask" (Scot Ruby)
• MVC is dead, it's time to MOVE on
• Domain Model Events - Ruby Tapas #21
• Getting Hexagonal with Wisper

Implementations

within one app

• event_bus
• wisper
• message_bus from discourse
• activerecord observers

between services

• kafka:
• amqp/rabbitmq
• websockets w/ faye

1-event_subscribers_initializer_or_global_config.rb

EventBus.
  subscribe(DonationReceipt.new).
  subscribe(NotifyAccountingSystem.new).
  subscribe(UpdatePublicStats.new).
  subscribe(LogInternalMetrics.new).
  subscribe(UpdateAnalyticsDashboard.new).
  subscribe(RealtimeViewerUpdate.new)

2-a-controller-like-thing.rb

class DonationsController # < ActionController::Base
  def create
    EventBus.subscribe(:donation_created) do |payload|
      send_user_to_payment_gateway(payload[:donation])
    end

    EventBus.subscribe(:donation_invalid) do |payload|
      render payload[:donation].errors, status: :bad_request
    end

    GiveDonation.new(current_user, params[:donation]).()
  end

  private
  def send_user_to_payment_gateway
    #...
  end
end

3-give_donation.rb

class GiveDonation
  attr_reader :donor,
    :donation,
    :event_bus

  def initialize(donor, donation_attributes, options={})
    @donor         = donor
    donation_class = options.fetch(:donation_class) { Donation }
    @donation      = donation_class.new(donation_attributes.merge(donor: donor))
    @event_bus     = options.fetch(:event_bus) { EventBus }
  end

  def call
    if donation.valid?
      donation.save!
      event_bus.broadcast(:donation_created, donation: donation)
    else
      event_bus.broadcast(:donation_invalid, donation: donation)
    end
  end
end

4-donation_receipt.rb

class DonationReceipt
  def donation_created(payload)
    Mailer.delay.send_donation_receipt(payload[:donation])
  end
end

5-notify_accounting_system.rb

class NotifyAccountingSystem
  def donation_created(payload)
    #..
  end
end