Rails3 で日付を「ago」と「since」で取得するメモ

(rails3.2.12)

irb(main):025:0> 1.day.ago
=> Wed, 20 Mar 2013 10:13:00 JST +09:00
irb(main):028:0> 7.days.since
=> Thu, 28 Mar 2013 10:13:22 JST +09:00
irb(main):029:0> 2.weeks.ago
=> Thu, 07 Mar 2013 10:13:31 JST +09:00
irb(main):030:0> 3.month.since
=> Fri, 21 Jun 2013 10:13:40 JST +09:00