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TimeWithZone comparison fails for distinct instances of same time

#3117

Let's say I have a model "Role" with timestamps and a string name attribute. I want to do some time comparisons. Here's the expected versus actual that I see:

Expected:

r = Role.create(:name => 'a role')
initial=r.created_at
r.reload
initial==r.created_at
=> true

Actual:

r=Role.create(:name => 'a role') => # initial = r.created_at => Sun, 30 Aug 2009 09:46:14 EDT -04:00 r.reload => # r.created_at == initial => false

I've tried <=>, converting to other types (Time, DateTime), and the comparison always fails. What's going on?

Reported by Ari Epstein · August 30th, 2009 @ 03:05 PM

State: invalid
Milestone: none
Assigned to: nobody
Importance: none

Activity

  1. Ari Epstein
    Ari Epstein
    • Tag set to activesupport, datetime, time, timewithzone

    August 30th, 2009 @ 03:05 PM

  2. Matt Duncan
    Matt Duncan

    I was unable to reproduce this on master.

    Loading development environment (Rails 3.0.pre)
>> r = Role.create(:name => 'a role')
=> #<Role id: 2, name: "a role", created_at: "2009-08-30 16:10:18", updated_at: "2009-08-30 16:10:18">
>> initial = r.created_at
=> Sun, 30 Aug 2009 16:10:18 UTC +00:00
>> r.reload
=> #<Role id: 2, name: "a role", created_at: "2009-08-30 16:10:18", updated_at: "2009-08-30 16:10:18">
>> initial == r.created_at
=> true

    August 30th, 2009 @ 05:12 PM

  3. Matt Jones
    Matt Jones

    I've seen this happen in tests before - typically caused by the database having a different time resolution than the system. So even though the two times print identically, one is really (for instance) 15:45:32.012445362 and the DB loads back 15:45:32, which doesn't compare as equal.

    September 5th, 2009 @ 05:42 AM

  4. JackC
    JackC

    Just ran into this in tests myself. You can determine the usec method to see the difference. I worked around this in my tests by specifying times instead of using the current time.

    October 5th, 2009 @ 07:47 PM

  5. Geoff Buesing
    Geoff Buesing
    • State changed from new to invalid

    Matt Jones is probably right; this looks to be an issue with the database not storing usec.

    In your tests, you can try coercing to_a before comparing; usec value isn't returned in the to_a representation:

    assert_equal initial.to_a, r.created_at.to_a

    October 27th, 2009 @ 02:34 AM