rails 更改預設的 dateformat Ref: http://www.ruby-doc.org/stdlib-1.9.3/libdoc/date/rdoc/DateTime.html#method-i-strftime

application.rb

# config/application.rb

module MyApp
  class Application < Rails::Application
    ...
    Time::DATE_FORMATS.merge!(:default => "%Y-%m-%d %H:%M", :ymd => "%Y-%m-%d", :md => "%m/%d", :week_day => "%u")
    ...
  end
end

usage.rb

User.last.created_at.to_s(:ymd)
Time.now.to_s(:week_day)