50 lines
2.3 KiB
Markdown
50 lines
2.3 KiB
Markdown
---
|
|
title: "Protip: TimeWithZone, All The Time"
|
|
date: 2008-09-10T00:00:00+00:00
|
|
draft: false
|
|
needs_review: true
|
|
canonical_url: https://www.viget.com/articles/protip-timewithzone-all-the-time/
|
|
---
|
|
|
|
If you've ever tried to retrieve a list of ActiveRecord objects based on
|
|
their timestamps, you've probably been bitten by the quirky time support
|
|
in Rails:
|
|
|
|
>> Goal.create(:description => "Run a mile") => #<Goal id: 1, description: "Run a mile", created_at: "2008-09-09 19:32:57", updated_at: "2008-09-09 19:32:57"> >> Goal.find(:all, :conditions => ['created_at < ?', Time.now]) => []
|
|
|
|
Huh? Checking the logs, we see that the two commands above correspond to
|
|
the following queries:
|
|
|
|
INSERT INTO "goals" ("updated_at", "description", "created_at") VALUES('2008-09-09 19:32:57', 'Run a mile', '2008-09-09 19:32:57') SELECT * FROM "goals" WHERE created_at < '2008-09-09 15:33:17'
|
|
|
|
Rails stores `created_at` relative to [Coordinated Universal
|
|
Time](https://en.wikipedia.org/wiki/Coordinated_Universal_Time), while
|
|
`Time.now` is based on the system clock, running four hours behind. The
|
|
solution? ActiveSupport's
|
|
[TimeWithZone](http://caboo.se/doc/classes/ActiveSupport/TimeWithZone.html):
|
|
|
|
>> Goal.find(:all, :conditions => ['created_at < ?', Time.zone.now]) => [#<Goal id: 1, description: "Run a mile", created_at: "2008-09-09 19:32:57", updated_at: "2008-09-09 19:32:57">]
|
|
|
|
**Rule of thumb:** always use TimeWithZone in your Rails projects. Date,
|
|
Time and DateTime simply don't play well with ActiveRecord. Instantiate
|
|
it with `Time.zone.now` and `Time.zone.local`. To discard the time
|
|
element, use `beginning_of_day`.
|
|
|
|
## BONUS TIP {#bonus_protip}
|
|
|
|
Since it's a subclass of Time, interpolating a range of TimeWithZone
|
|
objects fills in every second between the two times --- not so useful if
|
|
you need a date for every day in a month:
|
|
|
|
>> t = Time.zone.now => Tue, 09 Sep 2008 14:26:45 EDT -04:00 >> (t..(t + 1.month)).to_a.size [9 minutes later] => 2592001
|
|
|
|
Fortunately, the desired behavior is just a monkeypatch away:
|
|
|
|
class ActiveSupport::TimeWithZone def succ self + 1.day end end >> (t..(t + 1.month)).to_a.size => 31
|
|
|
|
For more information about time zones in Rails, [Geoff
|
|
Buesing](http://mad.ly/2008/04/09/rails-21-time-zone-support-an-overview/)
|
|
and [Ryan
|
|
Daigle](http://ryandaigle.com/articles/2008/1/25/what-s-new-in-edge-rails-easier-timezones)
|
|
have good, up-to-date posts.
|