What time is it? Or, handling timezones in Rails.
Posted by Wes in 
As a followup to a stack overflow answer, I thought I would give some examples of working with time zones in rails.
What does Rails timezone support do for me?
- Stores everything in UTC in the database
- Allows you to set an application default timezone and/or timezones for your users
- Automatically converts UTC in the database to the correct zone and back
What zones are available?
You can get a list of timezones with rake tasks:
# Displays names of all time zones recognized by the Rails TimeZone class, grouped by offset. rake time:zones:all # Displays names of time zones recognized by the Rails TimeZone class with the same offset as the system local time rake time:zones:local # Displays names of US time zones recognized by the Rails TimeZone class, grouped by offset. rake time:zones:us
Setting the default time zone
In your environment.rb (Rails 2) or application.rb (Rails 3) file, you can set the default timezone:
config.time_zone = 'Central Time (US & Canada)'
What does this do? By setting an application-wide timezone, any datetime will be stored in UTC in the database, but will be translated when we access it.
Set a timezone for a user
You can use time_zone_select to get a list of timezones for a user to pick from. The third argument is a list of “priority” zones that will appear first.
time_zone_select( "user", 'time_zone', TimeZone.us_zones, :default => "Pacific Time (US & Canada)")
Once the value is saved in the database, you’ll want to set it for each request, per user:
before_filter :set_timezone
def set_timezone
# current_user.time_zone #=> 'Central Time (US & Canada)'
Time.zone = current_user.time_zone || 'Central Time (US & Canada)'
end
[UPDATE: You'll need a field 'time_zone' in your user table!]
[UPDATE: You probably want to stay DRY and refer to the configured value instead of specifying the timezone value in both places:
Time.zone = current_user.time_zone || MyAppName::Application.config.time_zone]
Let me know if you have questions or improvements and I’ll integrate them into the article. Thanks!
Max says:
I put
1. before_filter :set_timezone
2.
3. def set_timezone
4. # current_user.time_zone #=> ‘Central Time (US & Canada)’
5. Time.zone = current_user.time_zone || ‘Central Time (US & Canada)’
6. end
in my application_controller.rb but when I always get this error:
undefined method ‘time_zone’ for #
I would appreciate if anyone could help me with this.
Damien White says:
Max,
I hope you figured out your problem. Your problem is that your user object doesn’t have a time_zone attribute. You can create a migration to fix that, and then just store the user’s time zone.
-Damien
George Anderson says:
You could also use “MyAppName::Application.config.time_zone” as the default. E.g.
Time.zone = current_user.time_zone || MyAppName::Application.config.time_zone
Then you would just have one single, unambiguous, authoritative representation of the default time zone (DRY).
Thanks for the post. Clear and concise.
Wes says:
@George: I considered that, but you’d have different syntaxes for Rails 2 and Rails 3. Added a note about referring to that, though, as it’s definitely the right way to do it.
Rhomobile and Timezone Info « programmingforeducation says:
[...] What time is it? Or, handling timezones in Rails [...]
Tom Harrison Jr says:
Awesome post, very helpful!
A quick note for Rails 3 users — the time_zone_select helper now is part of ActiveSuport, so must be qualified, as in
time_zone_select( "user", 'time_zone', ActiveSupport::TimeZone.us_zones, :default => "Pacific Time (US & Canada)")