[Ruby on Rails] Ruby Time.now vs Time.current

ruby에서 time zone 관련 요약

사용하지 말아야 하는 것 DON'T USE

* Time.now
* Date.Today
* Date.Today.to_time
* Time.parse("2021-10-21 18:19:20")
* Time.strptime(string, "%Y-%m-%dT%H:%M:%S%z")

사용해도 되는 것 DO USE

* Time.current
* 2.hours.ago
* Time.zone.today
* Date.current
* 1.day.from_now
* Time.zone.parse("2020-10-21 18:06:22")
* TIme.strptime(string, "%Y-%m-%dT%H:%M:%S%z").in_time_zone

 

Time zones in Rails

rails는 ruby와 같은 API를 제공하는데 rails에서 time zones 와 관련된 것을 볼 수 있다.

$ rails time:zones:all

* UTC -12:00 *
International Date Line West

...

* UTC +00:00 *
Casablanca
Dublin
Edinburgh
Lisbon
London
Monrovia
UTC

...

* UTC +09:00 *
Osaka
Sapporo
Seoul
Tokyo
Yakutsk

...

 

Three time zones

rails에서 3가지 time zones가 있다.

- system time

- application time

- database time 

# This is the time on my machine, also commonly described as "system time" (시스템 타임)
> Time.now
=> 2015-07-04 17:53:23 -0400

# Let's set the time zone to be Fiji (피지의 타임존으로 등록해도)
> Time.zone = "Fiji"
=> "Fiji"

# But we still get my system time (여전히 시스템 타임이 출력)
> Time.now
=> 2015-07-04 17:53:37 -0400

# However, if we use `zone` first, we finally get the current time in Fiji (타임존을 등록)
> Time.zone.now
=> Sun, 05 Jul 2015 09:53:42 FJT +12:00

# We can also use `current` to get the same
> Time.current
=> Sun, 05 Jul 2015 09:54:17 FJT +12:00

# Or even translate the system time to application time with `in_time_zone`
> Time.now.in_time_zone
=> Sun, 05 Jul 2015 09:56:57 FJT +12:00

# Let's do the same with Date (we are still in Fiji time, remember?)
# This again is the date on my machine, system date
> Date.today
=> Sat, 04 Jul 2015

# But going through `zone` again, and we are back to application time
> Time.zone.today
=> Sun, 05 Jul 2015

# And gives us the correct tomorrow according to our application's time zone
> Time.zone.tomorrow
=> Mon, 06 Jul 2015

# Going through Rails' helpers, we get the correct tomorrow as well
> 1.day.from_now
=> Mon, 06 Jul 2015 10:00:56 FJT +12:00

 

[출처]

https://thoughtbot.com/blog/its-about-time-zones

It's About Time (Zones)