attributes_for_update

# File activerecord/lib/active_record/attribute_methods.rb, line 472
      def attributes_for_update(attribute_names)
        attribute_names &= self.class.column_names
        attribute_names.delete_if do |name|
          self.class.readonly_attribute?(name) ||
            self.class.counter_cache_column?(name) ||
            column_for_attribute(name).virtual?
        end
      end