[RUBY] Which class should I use to get the date and time in my Rails app (Time, DateTime, TimeWithZone)

Which class should be used to get the date and time

--Time class --DateTime class --TimeWithZone class

In Rails, unless you have a specific reason It is better to unify with the TimeWithZone class rather than the Time class and DateTime class.

About time zone

There are three places to set the time zone.

--System --Environment variable ╩╗ENV ['TZ'] `

Use Time.zone.name to see which timezone is set in application.rb.

# application.rb
config.time_zone = 'Tokyo'

=> "Tokyo"

Which time zone will be used

To complicate matters, the time zone used depends on the class and the methods associated with it. For example Time.now using the method now related to the Time class uses the timezone of the environment variable Time.current using the method current associated with the Time class uses the timezone of application.rb.

#Environment variables are used and class becomes Time
[1] pry(main)> Time.now
=> 2020-07-31 19:39:18 +0900
[2] pry(main)> Time.now.class
=> Time

#application.rb is used and class becomes TimeWithZone
[3] pry(main)> Time.current
=> Fri, 31 Jul 2020 19:39:35 JST +09:00
[4] pry(main)> Time.current.class
=> ActiveSupport::TimeWithZone

Use Time.current or Time.zone.now to get the current date and time

There are the following methods to get the current date and time.

  1. Time.now (use the timezone of the environment variable)
  2. DateTime.now (use the timezone of the environment variable)
  3. Time.current (use the timezone of application.rb)
  4. Time.zone.now (use the timezone in application.rb)

In conclusion, it's better to use the TimeWithZone class 3 or 4 (because if you want to make it an international application, you can handle it in various ways).

#The timezone of the environment variable is used
[1] pry(main)> Time.now
=> 2020-07-31 19:43:14 +0900 #Time class
[2] pry(main)> DateTime.now
=> Fri, 31 Jul 2020 19:43:21 +0900 #DateTime class

# application.rb timezone is used
[3] pry(main)> Time.current
=> Fri, 31 Jul 2020 19:43:26 JST +09:00 #ActiveSupport::TimeWithZone class
[4] pry(main)> Time.zone.now
=> Fri, 31 Jul 2020 19:43:32 JST +09:00 #ActiveSupport::TimeWithZone class

Reference article

I referred to the following article. The article explains it in great detail. https://qiita.com/jnchito/items/cae89ee43c30f5d6fa2c

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