Pull in Viget posts

content/elsewhere/protip-timewithzone-all-the-time/index.md

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+---
+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.