ActiveRecord callback setup from different model

Let's say I have to simple models First and Second, and there is one to one relationship from Second using belongs_to :first. Now I want to do something with Second, when First is saved. But I don't want to setup an after_save callback in First, to deal with Second.

I want to keep my models clean, and unaware of each other as much as possible. I'm always following best practice开发者_StackOverflow中文版s in object encapsulation, and it makes my life easier, always.

So naturally, since after_save is a class method, I tried to setup this callback in Second, like this:

class Second < ActiveRecord::Base

  belongs_to :first

  First.after_save do |record|
    if that = Second.find_by_first_id(record.id)
      # grow magic mushrooms here...
    end
  end
end

but this doesn't work, that callback is never executed, and no error is raised.

You may do it via observer:

class FirstObserver < ActiveRecord::Observer
  def after_save(first)
    ...
  end
end

Don't forget to enable observer in your config/application.rb:

config.active_record.observers = :first_observer

It might be best to set up an observer, something like "FirstObserver" and write an after-save callback there.

Try this one:

First.class_eval do
  def after_save record
     #mashrooooms
  end
end