update_with_lock

# File activerecord/lib/active_record/locking/optimistic.rb, line 69
        def update_with_lock(attribute_names = @attributes.keys) #:nodoc:
          return update_without_lock(attribute_names) unless locking_enabled?

          lock_col = self.class.locking_column
          previous_value = send(lock_col).to_i
          send(lock_col + '=', previous_value + 1)

          attribute_names += [lock_col]
          attribute_names.uniq!

          begin
            affected_rows = connection.update("UPDATE \#{self.class.quoted_table_name}\nSET \#{quoted_comma_pair_list(connection, attributes_with_quotes(false, false, attribute_names))}\nWHERE \#{self.class.primary_key} = \#{quote_value(id)}\nAND \#{self.class.quoted_locking_column} = \#{quote_value(previous_value)}\n", "#{self.class.name} Update with optimistic locking")

            unless affected_rows == 1
              raise ActiveRecord::StaleObjectError, "Attempted to update a stale object"
            end

            affected_rows

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