Save Datetime in UTC, view/query in User's timezone in Rails? - ruby-on-rails

Question

What is the standard for saving times in one zone and viewing them in another? I have this in my environment.rb:
config.time_zone = 'UTC'
But I want to render it, and do queries like "all posts created today" in their timezone, where beginning_of_day returns the beginning of the day in their timezone rather than UTC. Is rails already handling the conversion in the background?
Here's the issue:
#now = Time.now
=> Wed Jan 26 09:50:04 -0600 2011
User.count(:conditions => ["created_at > ?", #now])
SQL (1.3ms) SELECT count(*) AS count_all FROM `users` WHERE (created_at > '2011-01-26 09:50:04')
=> 1
#now = Time.now.utc
=> Wed Jan 26 15:50:10 UTC 2011
User.count(:conditions => ["created_at > ?", #now])
SQL (1.2ms) SELECT count(*) AS count_all FROM `users` WHERE (created_at > '2011-01-26 15:50:10')
=> 0

Answer 1

ActiveSupport has built-in methods to display time values in any time zone. Typically you'd add a time_zone column to your User model and set it to the user's preferred zone.
#user.update_attribute(:time_zone,'Eastern Time (US & Canada)')
Then when displaying a time value, set the zone to the user's zone.
Time.zone = #user.time_zone
Time.zone.now # shows current time according to #user.time_zone
One approach is to set this in ApplicationController so it is done for each request:
class ApplicationController < ActionController::Base
before_filter :set_time_zone
def set_time_zone
Time.zone = current_user.time_zone if current_user
end
end
Note: see the API under ActiveSupport::TimeWithZone