#106 Time Zones (revised)

Be careful not to cache pages which might be common to users with different timezones. Or use javascript to change the times on the client side.

@ryanb, can you please elaborate a bit more about the leaky before filter? It's convenient that time accepts a block so around filter fits in perfectly, but i was just curious about the leaky before filter comment.

This episode will help solidify a lot of testing headaches. We're currently using javascript to manipulate time zones but I think this episode provides great in depth insight into how to manipulate time zones for testing. Thanks Ryan.

If you want to get a time with a specific time zone, you can do:

ActiveSupport::TimeZone.new("Asia/Tokyo").local(2012, 1, 1)  # => Sun, 01 Jan 2012 00:00:00 JST +09:00

Keep in mind that if you do things in a different ruby process (e.g. background jobs) you need to set the correct timezone there too.

I was wondering about Time.use_zone resp Time.zone in a threaded environment
(like torquebox/jruby).

If I interpret the documentation correctly, then Time.zone is a thread local
variable, which means it will just work fine. Can somebody confirm this?

Also the docu reads that Time.zone is a per request value (in mri). However,
that would mean that you actually don't need to use an around filter. A before
filter should suffice, doesn't it?

You can also use Time.current to get time in default time zone.
https://github.com/rails/rails/blob/.../activesupport/lib/active_support/core_ext/time/calculations.rb#L45

FWIW, I implemented a simple around_filter as shown here in my ApplicationController and it has massively slowed down my requests:

  around_filter :use_time_zone

  private

  def use_time_zone(&block)
    Time.use_zone('Eastern Time (US & Canada)', &block)
  end

I've never had an issue using before_filter when setting time zone. Its local.

Great episode, building off this for auto detection...
** How do you convert js values received as TZInfo identifiers to Rails TimeZone name/key? **

FROM: "America/New_York" returned from JavaScript TZinfo detection
TO: "Eastern Time (US & Canada)" convention used in Rails TimeZone

http://stackoverflow.com/questions/14221615/how-to-convert-tzinfo-identifier-to-rails-timezone-name-key

Thanks!
-E

I'm using the code introduced in this tutorial, and validation of the time_zone field fails with the error: Time zone is not included in the list.

#--- View ---
f.label :time_zone
f.time_zone_select :time_zone, ActiveSupport::TimeZone.us_zones

#--- Model ---
validates_inclusion_of :time_zone, in: ActiveSupport::TimeZone.zones_map(&:name)

Has anyone else encountered this?

I'm using RailsAdmin and got the following error:

undefined method `klass' for nil:NilClass
app/controllers/application_controller.rb:26:in `user_time_zone'

What went wrong?

I am trying to query all of the Users that share a common time zone offset (so I can send them an email at a particular time everyday), and can not figure it out!

User.where(:time_zone => ['list','of time','zone names'])

How do I get a list of the time zone names for a particular offset? I've been tinkering with TzInfo and ActiveSupport::TimeZone.zones_map with limited success.

Am I taking the wrong approach here? I was thinking I could store the GMT offset on the user instead, and query that way?

My google-fu has let me down on this one.

In a model I only want to find those which didn't expire, yet.

For that I have a scope:

# Mongoid
scope :live, gt(ends_at: Time.now)

Should I use Time.current instead? I don't feel like I got the point :)
When I set this variable :ends_at, should I use Time.current + 30.days ?

Thx for the great work!

You say:

"It’s a good idea to use a time zone that matches the one where most of our app’s users are located"

Why is that? As also noted, it's a good idea to use a different time zone for development so errors aren't obfuscated. So why not just leave config.time_zone at UTC? It seems like setting current time zone is only useful when all users are in the same time zone. Otherwise, it just adds complexity. Am I missing something?

Just a follow up on the issue with before_filter - if we set the time zone using before_filter at the top of the ApplicationController then why should bother about leaking it through to the whole process? Every new request to our application will go through the controller and for each new request the proper time zone should be set again right? We just need to make sure that it's always set and fallbacks to some default. Workers can handle time zone in a different way.

In Rails 4.1, we can no longer use this line:

validates_inclusion_of :time_zone, in: ActiveSupport::TimeZone.zones_map(&:name)

It needs to be:

validates_inclusion_of :time_zone, in: ActiveSupport::TimeZone.zones_map(&:name).keys

as discussed here

It is useful when reading these articles, I have a few days to find these things. It too is excellent, very grateful for your profound contribution

Since the prior request most likely had a workflow that ran the before filter, and since the before filter sets the time zone for the entire process, that time zone is now being used for any code running in that process.