define_callback

# File activerecord/lib/active_record/associations/builder/collection_association.rb, line 49
      def define_callback(callback_name)
        full_callback_name = "#{callback_name}_for_#{name}"

        # TODO : why do i need method_defined? I think its because of the inheritance chain
        model.class_attribute full_callback_name.to_sym unless model.method_defined?(full_callback_name)
        model.send("#{full_callback_name}=", Array.wrap(options[callback_name.to_sym]))
      end