Modifying the timezone in Ruby or with ActiveSupport

Sometimes you may need to query an SQL record in ruby and convert the UTC time into a local timezone. This is usually done in a framework like Ruby on Rails. Many web frameworks use the Active Support gem. From their enhanced tooling, they may set the timezone on the thread by calling:

Time.zone = "Requests Time Zone".

The Time class in ruby (w/ ActiveSupport) can then access this by calling the getter method:

Time.zone

Here are some examples of how this plays out in action.

	require 'Time'
	utc_time_str = '2020-01-02T18:16:35+0000'
	# Outputs UTC time.
	Time.parse(utc_time_str)
	=> 2020-01-02 18:16:35 +0000
	# Outputs system timezone. Also can use to_time
	Time.parse(utc_time_str).to_localtime
	=> 2020-01-02 13:16:35 -0500
	# With ActiveSupport you can set the current threads time zone.
	# This is how RoR handles setting time zones on web requests.
	require 'active_support/all'
	# Start with a UTC time (say from an SQL query.
	# NOTE: No time zone info in string.
	utc_time_str = '2020-1-2 18:16:35'
	# Parse time from SQL query declaring as UTC TZ.
	utc_time = Time.find_zone('UTC').parse(utc_time_str)
	=> Thu, 02 Jan 2020 18:16:35 UTC +00:00
	# Set the timezone to convert to. This is done in the request in RoR.
	Time.zone = 'Central Time (US & Canada)'
	Time.zone.parse(utc_time.to_s)
	=> Thu, 02 Jan 2020 12:16:35 CST -06:00

view raw utc_to_localtime.rb hosted with ❤ by GitHub

See the TimeZone documentation if you need more info. Hope this may be helpful and please comment if you have any questions or additional advice!