subject = Subject.new(name:"First Subject", position: 1, visible: true)

irb(main):008:0* subject.save
   (0.2ms)  BEGIN
  SQL (2.8ms)  INSERT INTO `subjects` (`name`, `position`, `visible`, `created_at`, `updated_at`) VALUES ('First Subject', 1, 1, '2016-04-16 01:52:31', '2016-04-16 01:52:31')
   (1.5ms)  COMMIT

irb(main):008:0* subject
=> #<Subject id: 1, name: "First Subject", position: 1, visible: true, created_at: "2016-04-16 01:52:31", updated_at: "2016-04-16 01:52:31">

本來是在10​​點左右保存的，但是裡面的created_at, updated_at時間是1點，不和系統時間一致。