module ActiveModel::Callbacks

def define_model_callbacks(*callbacks)

!, ? or =.
NOTE: +method_name+ passed to +define_model_callbacks+ must not end with

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

end
before_create AnotherClass

define_model_callbacks :create
extend ActiveModel::Callbacks
class MyModel

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

only.
Would create +after_create+, +before_update+, and +around_destroy+ methods

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

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

define_model_callbacks :initialize, only: :after

around or after) or just some.
:only option, where you can choose if you want all types (before,
in case you want to overwrite a default. Besides that, it also accepts an
+define_model_callbacks+ accepts the same options +define_callbacks+ does, 
def define_model_callbacks(*callbacks)
  options = callbacks.extract_options!
  options = {
    skip_after_callbacks_if_terminated: true,
    scope: [:kind, :name],
    only: [:before, :around, :after]
  }.merge!(options)
  types = Array(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