How to Change the Zone Offset for a Time in Ruby on Rails

How do I change the zone offset for a time in Ruby on Rails?

I'm using Rails 2.0 before they added the code that makes weppos solution work. Here's what I did

# Silly hack, because sometimes the input_date is in the wrong timezone
temp = input_date.to_time.to_a
temp[8] = true
temp[9] = "Eastern Daylight Time"
input_date = Time.local(*temp)

I break the time down into a 10 element array, change the timezone and then convert the array back into a time.

Set time zone offset in Ruby

Change the time zone on your OS; Ruby will pick up the change.

Ruby / Rails - Change the timezone of a Time, without changing the value

Sounds like you want something along the lines of

ActiveSupport::TimeZone.new('America/New_York').local_to_utc(t)

This says convert this local time (using the zone) to utc. If you have Time.zone set then you can of course to

Time.zone.local_to_utc(t)

This won't use the timezone attached to t - it assumes that it's local to the time zone you are converting from.

One edge case to guard against here is DST transitions: the local time you specify may not exist or may be ambiguous.

How do you get the local timezone offset in +hh:mm format?

strftime with %z (: means hour and minute offset from UTC with a colon):

Time.current.strftime("%:z")

Change Time zone in pure ruby (not rails)

You can use the Time extensions from Active Support outside of Rails:

require 'active_support/core_ext/time'

t = Time.now
#=> 2014-08-15 15:38:56 +0200

t.in_time_zone('Pacific Time (US & Canada)')
#=> Fri, 15 Aug 2014 06:38:56 PDT -07:00

Now you can do

class Time
  def to_pst
    in_time_zone('Pacific Time (US & Canada)')
  end
end

t = Time.now
#=> 2014-08-15 15:42:39 +0200

t.to_i
#=> 1408110159

t.to_pst
#=> Fri, 15 Aug 2014 06:42:39 PDT -07:00

t.to_pst.to_i
#=> 1408110159

# timestamp does not change!

Additionally you might also want the time extensions on Numeric and Date:

require 'active_support/core_ext/date'
require 'active_support/core_ext/numeric/time'

2.days.from_now
#=> 2014-08-17 15:42:39 +0200

Time zone offset select

There are no such built-in Rails helpers, but it's easy to implement with options_for_select

options_for_select(ActiveSupport::TimeZone.us_zones.map {|zone| zone.utc_offset / 3600}.uniq)

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