DateTime vs Time and ActiveRecord

example.md

>> ps.cancel_at
=> Fri, 05 Oct 2012 00:00:00 UTC +00:00
>> ps.cancel_at.class
=> ActiveSupport::TimeWithZone
>> ps.cancel_at = DateTime.new 2012, 11, 05
=> Mon, 05 Nov 2012 00:00:00 +0000
>> ps.save
   (0.2ms)  BEGIN
  Entity Load (0.5ms)  SELECT "entities".* FROM "entities" WHERE "entities"."id" = 2485 LIMIT 1
  Product Load (0.7ms)  SELECT "products".* FROM "products" WHERE "products"."id" = 32445 LIMIT 1
   (0.8ms)  UPDATE "product_subscriptions" SET "cancel_at" = '2012-11-05 00:00:00.000000', "updated_at" = '2012-10-05 22:16:42.029113' WHERE "product_subscriptions"."id" = 6762
   (1245.9ms)  COMMIT
=> true
>> ps.cancel_at = Time.local 2012, 11, 05
=> 2012-11-05 00:00:00 -0700
>> ps.save
   (0.2ms)  BEGIN
   (0.5ms)  UPDATE "product_subscriptions" SET "cancel_at" = '2012-11-05 07:00:00.000000', "updated_at" = '2012-10-05 22:17:32.097390' WHERE "product_subscriptions"."id" = 6762
   (0.4ms)  COMMIT
=> true
>> 

Dates with time zone are good for when things happened, but not necessarily for scheduling, such as a due date.

Consider setting something due for Oct 5th mountain time, beginning of day. That task will appear due for your colleague in Pacific time on the 4th, which is super confusing unless you display the time along with it.

It's not necessarily that a due date is bad for dates with time zone. Maybe something needs to be finished by end of work day... you'd set the timestamp to `2012-10-05 6:00 PM MDT' and i would make sense for you and any others looking since it's due by that exact time.

The issue comes up when you have a date but are storing it as a datetime. Your nice "October 5th" date gets a silent "at midnight" appended to it, which messes with your coordination between time zones. If you don't intend to use a value as a DateTime then the database should store it as a Date

... Assuming Date objects in the database don't come with timezone support.

Something we could consider is our nice_date helper, perhaps adding a precise_date which normalizes to a set TZ regardless of logged_in user's TZ.

>> Time.utc(2012, 8, 13, 5, 0).in_time_zone(-6.hours).to_date
=> Sun, 12 Aug 2012
>> Time.utc(2012, 8, 13, 5, 0).to_date
=> Mon, 13 Aug 2012
>>