update_counters (ActiveRecord::Base)

    # File lib/active_record/base.rb, line 903
          def update_counters(id, counters)
            updates = counters.inject([]) { |list, (counter_name, increment)|
              sign = increment < 0 ? "-" : "+"
              list << "#{connection.quote_column_name(counter_name)} = COALESCE(#{connection.quote_column_name(counter_name)}, 0) #{sign} #{increment.abs}"
            }.join(", ")
            update_all(updates, "#{connection.quote_column_name(primary_key)} = #{quote_value(id)}")
          end