Variation of RubyTapas episode "021 Domain Model Events" without using callbacks or reimplementing dirty tracking.

tasks_controller_refactoring.rb

class TasksController < ApplicationController
  def update
    if @task.update_attributes(params[:task])
      TaskPusher.new(@task, socket_id).push_changes
      TaskMailSender.new(@task, current_user).deliver_email
      # success response
    else
      # failure respond
    end
  end
end

class TaskPusher < Struct.new(:task, :socket_id)
  def push_changes
    if changed?("assignee")
      # push assignee changes
    end
    if changed?("project_id")
      # push project changes
    end
  end

  def changed?(attribute)
    if changes = task.previous_changes[attribute]
      changes.first != changes.last
    end    
  end
end

class TaskMailSender < Struct.new(:task, :recipient)
  def deliver_email
    if changed?("status")
      # email status change
    end
    if changed?("assignee")
      # email assignee change
    end
  end

  def changed?(attribute)
    if changes = task.previous_changes[attribute]
      changes.first != changes.last
    end    
  end
end

And keeping the tracker object.

Nice.

Just realized a big issue with using previous_changes. What if the TaskPusher ends up saving the task again? Then the TaskMailSender would not detect the earlier changes.