datetime.rb

class DateTime
  @@date_formats = {
          :db => "%Y-%m-%d %H:%M:%S",
          :time => "%H:%M",
          :short => "%d %b %H:%M",
          :long => "%B %d, %Y %H:%M",
          :long_ordinal => lambda { |time| time.strftime("%B 
  #{time.day.ordinalize}, %Y %H:%M") },
          :rfc822 => "%a, %d %b %Y %H:%M:%S %z"
        }

  alias :old_to_s :to_s
  def to_s(format = nil)
    return old_to_s unless format
    self.strftime(@@date_formats[format.to_sym])
  end
end