Ruby:Change UTC time zone to UTC+ or UTC - zone - ruby-on-rails

Question

I want to convert the utc time to 'utc+1' or 'utc+something' time zone and convert back that to utc time zone.
Its something like that what i want to do. I am asking user to choose there UTC time zone ex: utc+4 .and i am getting current UTC time using Time.now.utc .Now i wwant to convert this utc time to 'utc+4'.
And after displaying that time to 'utc+4' i want to convert back that time equivalent utc time zone.
How this can be done?

Answer 1

If you are working with Ruby On Rails and you want to change time zone per request and reset it back after finishing the request. You can use Time.use_zone to set the time zone for the user (document: http://api.rubyonrails.org/classes/Time.html#method-i-use_zone)
The following is what I have tested in Rails 4.1.
First, It is recommended to set the sane default for config.time_zone (in config/application.rb), I set to "Mumbai" (UTC+5.30) for instance. (to list time zones, you can use command bundle exec rake time:zones:all)
module MyApp
class Application < Rails::Application
config.time_zone = 'Mumbai'
end
end
In your project, run rails g model User name:string time_zone:string
And bundle exec rake db:migrate
Then, create some test users via rails console, run rails c
Loading development environment (Rails 4.1.4)
irb(main):001:0> first_user = User.create!(name: 'zdk', time_zone: 'Bangkok')
(0.1ms) begin transaction
SQL (0.4ms) INSERT INTO "users" ("created_at", "name", "time_zone", "updated_at") VALUES (?, ?, ?, ?) [["created_at", "2014-07-31 09:21:13.750710"], ["name", "zdk"], ["time_zone", "Bangkok"], ["updated_at", "2014-07-31 09:21:13.750710"]]
(0.6ms) commit transaction
=> #<User id: 1, name: "zdk", time_zone: "Bangkok", created_at: "2014-07-31 09:21:13", updated_at: "2014-07-31 09:21:13">
irb(main):002:0> second_user = User.create!(name: 'joe', time_zone: 'London')
(0.1ms) begin transaction
SQL (0.8ms) INSERT INTO "users" ("created_at", "name", "time_zone", "updated_at") VALUES (?, ?, ?, ?) [["created_at", "2014-07-31 09:21:31.299606"], ["name", "joe"], ["time_zone", "London"], ["updated_at", "2014-07-31 09:21:31.299606"]]
(1.9ms) commit transaction
=> #<User id: 2, name: "joe", time_zone: "London", created_at: "2014-07-31 09:21:31", updated_at: "2014-07-31 09:21:31">
irb(main):003:0>
Try to query what we just created, you can see that it uses time zone that you have set in Application config (config.time_zone).
The output:
irb(main):003:0> first_user.created_at
=> Thu, 31 Jul 2014 14:51:13 IST +05:30
irb(main):005:0> second_user.created_at
=> Thu, 31 Jul 2014 14:51:31 IST +05:30
And how to handle per request basis time zone using Time.zone.
Go to your ApplicationController (app/controllers/application_controller.rb file).
Create a method that set time zone called by around_filter ( More details: http://www.elabs.se/blog/36-working-with-time-zones-in-ruby-on-rails ). I also create hello action will be routed from root url. Like so:
class ApplicationController < ActionController::Base
protect_from_forgery with: :exception
around_filter :set_time_zone
def set_time_zone
if true #if user loggin ?
#user = User.first #Change to User.last to see the result.
Time.use_zone(#user.time_zone) { yield }
else
yield
end
end
def hello
render plain: "Hello, user: #{#user.name}. Created: #{#user.created_at}"
end
end
Routing application uri to your controller method by editing your config routes (config/routes.rb) to have following this
Rails.application.routes.draw do
root 'application#hello'
end
If you set everything correctly. You should have the output in this format
for the first user: Hello, user: zdk. Created: <Date> <Time> +0700
for the second user: Hello, user: joe. Created: <Date> <time> +0100
In summary, the flow is something like:
+------------+
| APP |
+------------+
+ Use the Time.zone value instead if it's set
| ^
WRITE |
v | READ
+
Convert to UTC Convert from UTC to config.time_zone
+ ^
| |
WRITE | READ
| |
v +
+--------------------------------+
| |
| DB |
| |
| UTC |
+--------------------------------+
Hope this helps.

Answer 2

You can use ActiveSupport::TimeWithZone
Example :
#Define a TimeZone
Time.zone = 'Eastern Time (US & Canada)' # => 'Eastern Time (US & Canada)'
#Define a utc time
t = Time.utc(2007, 2, 10, 20, 30, 45) # => '2007-02-10 20:30:45 UTC
#same time with gmt -5
t.in_time_zone # => Sat, 10 Feb 2007 15:30:45 EST -5:00