Active Model Callbacks

Provides an interface for any class to have Active Record like callbacks.

Like the Active Record methods, the callback chain is aborted as soon as one of the methods in the chain returns false.

First, extend ActiveModel::Callbacks from the class you are creating:

class MyModel
  extend ActiveModel::Callbacks
end

Then define a list of methods that you want callbacks attached to:

define_model_callbacks :create, :update

This will provide all three standard callbacks (before, around and after) for both the :create and :update methods. To implement, you need to wrap the methods you want callbacks on in a block so that the callbacks get a chance to fire:

def create
  run_callbacks :create do
    # Your create action methods here
  end
end

Then in your class, you can use the before_create, after_create and around_create methods, just as you would in an Active Record module.

before_create :action_before_create

def action_before_create
  # Your code here
end

You can choose not to have all three callbacks by passing a hash to the #define_model_callbacks method.

define_model_callbacks :create, :only => [:after, :before]

Would only create the after_create and before_create callback methods in your class.

Methods
D
E
Included Modules
Class Public methods
extended(base)

Source: show | on GitHub 

# File activemodel/lib/active_model/callbacks.rb, line 49
def self.extended(base)
  base.class_eval do
    include ActiveSupport::Callbacks
  end
end
Instance Public methods
define_model_callbacks(*callbacks)

#define_model_callbacks accepts the same options define_callbacks does, in case you want to overwrite a default. Besides that, it also accepts an :only option, where you can choose if you want all types (before, around or after) or just some.

define_model_callbacks :initializer, :only => :after

Note, the :only => <type> hash will apply to all callbacks defined on that method call. To get around this you can call the #define_model_callbacks method as many times as you need.

define_model_callbacks :create, :only => :after
define_model_callbacks :update, :only => :before
define_model_callbacks :destroy, :only => :around

Would create after_create, before_update and around_destroy methods only.

You can pass in a class to before_<type>, after_<type> and around_<type>, in which case the callback will call that class’s <action>_<type> method passing the object that the callback is being called on.

class MyModel
  extend ActiveModel::Callbacks
  define_model_callbacks :create

  before_create AnotherClass
end

class AnotherClass
  def self.before_create( obj )
    # obj is the MyModel instance that the callback is being called on
  end
end

Source: show | on GitHub 

# File activemodel/lib/active_model/callbacks.rb, line 88
def define_model_callbacks(*callbacks)
  options = callbacks.extract_options!
  options = {
     :terminator => "result == false",
     :scope => [:kind, :name],
     :only => [:before, :around, :after]
  }.merge(options)

  types = Array.wrap(options.delete(:only))

  callbacks.each do |callback|
    define_callbacks(callback, options)

    types.each do |type|
      send("_define_#{type}_model_callback", self, callback)
    end
  end
end