in programming/rdoc/rdoc-example.rb [106:113]
def update_counters(id, counters)
updates = counters.inject([]) { |list, (counter_name, increment)|
sign = increment < 0 ? "-" : "+"
list << "#{connection.quote_column_name(counter_name)} = #{connection.quote_column_name(counter_name)} #{sign} #{increment.abs}"
}.join(", ")
update_all(updates, "#{connection.quote_column_name(primary_key)} = #{quote_value(id)}")
end