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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?

neo-code
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2 Answers2

4

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.

zdk
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1

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
Yann VERY
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