_update_record

# File activerecord/lib/active_record/locking/optimistic.rb, line 78
        def _update_record(attribute_names = self.attribute_names) #:nodoc:
          return super unless locking_enabled?
          return 0 if attribute_names.empty?

          lock_col = self.class.locking_column
          previous_lock_value = send(lock_col).to_i
          increment_lock

          attribute_names += [lock_col]
          attribute_names.uniq!

          begin
            relation = self.class.unscoped

            affected_rows = relation.where(
              self.class.primary_key => id,
              lock_col => previous_lock_value,
            ).update_all(
              Hash[attributes_for_update(attribute_names).map do |name|
                [name, _read_attribute(name)]
              end]
            )

            unless affected_rows == 1
              raise ActiveRecord::StaleObjectError.new(self, "update")
            end

            affected_rows

          # If something went wrong, revert the version.
          rescue Exception
            send(lock_col + '=', previous_lock_value)
            raise
          end
        end