Callbacks are hooks into the lifecycle of an object that allow you to trigger logic before or after an alteration of the object state.

Mixing in this module allows you to define callbacks in your class.

Example: 

  class Storage
    include ActiveSupport::Callbacks

    define_callbacks :before_save, :after_save
  end

  class ConfigStorage < Storage
    before_save :saving_message
    def saving_message
      puts "saving..."
    end

    after_save do |object|
      puts "saved"
    end

    def save
      run_callbacks(:before_save)
      puts "- save"
      run_callbacks(:after_save)
    end
  end

  config = ConfigStorage.new
  config.save

Output: 

  saving...
  - save
  saved

Callbacks from parent classes are inherited.

Example: 

  class Storage
    include ActiveSupport::Callbacks

    define_callbacks :before_save, :after_save

    before_save :prepare
    def prepare
      puts "preparing save"
    end
  end

  class ConfigStorage < Storage
    before_save :saving_message
    def saving_message
      puts "saving..."
    end

    after_save do |object|
      puts "saved"
    end

    def save
      run_callbacks(:before_save)
      puts "- save"
      run_callbacks(:after_save)
    end
  end

  config = ConfigStorage.new
  config.save

Output: 

  preparing save
  saving...
  - save
  saved
Methods
Classes and Modules
Module ActiveSupport::Callbacks::ClassMethods
Class ActiveSupport::Callbacks::Callback
Class ActiveSupport::Callbacks::CallbackChain
Public Class methods
included(base)

[ show source ]

     # File activesupport/lib/active_support/callbacks.rb, line 200
200:     def self.included(base)
201:       base.extend ClassMethods
202:     end
Public Instance methods
run_callbacks(kind, options = {}, &block)

Runs all the callbacks defined for the given options.

If a block is given it will be called after each callback receiving as arguments: 

 * the result from the callback
 * the object which has the callback

If the result from the block evaluates to false, the callback chain is stopped.

Example: 

  class Storage
    include ActiveSupport::Callbacks

    define_callbacks :before_save, :after_save
  end

  class ConfigStorage < Storage
    before_save :pass
    before_save :pass
    before_save :stop
    before_save :pass

    def pass
      puts "pass"
    end

    def stop
      puts "stop"
      return false
    end

    def save
      result = run_callbacks(:before_save) { |result, object| result == false }
      puts "- save" if result
    end
  end

  config = ConfigStorage.new
  config.save

Output: 

  pass
  pass
  stop

[ show source ]

     # File activesupport/lib/active_support/callbacks.rb, line 276
276:     def run_callbacks(kind, options = {}, &block)
277:       self.class.send("#{kind}_callback_chain").run(self, options, &block)
278:     end