rails activerecord observer usage

要使Observer工作，第一种做法是在controller里声明， 这样unit test就无法加载此observer到console中

# app/models/flower_observer.rb
class FlowerObserver < ActiveRecord::Observer
  observe Flower

  def after_create(model)
    # model.do_something!
  end
end

# controller(s)
class FlowerController < ApplicationController
  observer :flower_observer
end

第二种做法可以加载observer到console中：

# app/models/foo_bar.rb
class FooBar < ActiveRecord::Base
end

FooBarObserver.instance

最后一个方法是在config/environment.rb中加载此observer:

config.active_record.observers = :flower_observer