model callbacks of Rails ActiveRecord

class Encrypter
  def before_save(model)
    model.name.tr! 'a-z', 'b-za'
  end

  def after_save(model)
    model.name.tr! 'b-za', 'a-z'
  end

  # alias_method :after_find, :after_save
  # alias_method 
  # Makes new_id a new copy of the method old_id. This can be used to retain access to 
  # methods that are overridden.   

  alias after_find after_save
  # Aliasing 
  # alias new_name old_name 
  # creates a new name that refers to an existing method, operator, global variable, or reg- 
  # ular expression backreference ($&, $`, $', and $+). Local variables, instance variables, 
  # class variables, and constants may not be aliased. The parameters to alias may be 
  # names or symbols.

end

class ActiveRecord::Base
  def self.encrypted
    encrypt = Encrypter.new
    before_save encrypt
    after_save encrypt
    after_find encrypt
    module_eval <<-"end_eval"
      def after_find
        # Unlike all the other callbacks, after_find and after_initialize will only be run 
        # if an explicit implementation is defined (def after_find).
      end
    end_eval
  end
end

class User < ActiveRecord::Base
  encrypted
  protected
  def validate_on_create()
    puts 'existed user name' if self.class.exists? :name => name
  end
end