Skip to content


config.time_zone and datetime update #3965

schiza opened this Issue · 14 comments

9 participants


In my application I have: config.time_zone = 'Warsaw'

A strange issue I have, is that it seems like Rails are having problems with comparision of datetime fields.
If I change the datetime 1 hour back (and Warsaw is currently in timezone +0100), Rails won't update the database, even if the field has changed. However, if I change the field once again, then the update will go to the database.
(Rails 3.1.0, ruby-1.9.2-p290, fresh rails app):

$ rails g model User starts_at:datetime
$ rake db:migrate
$ rails c
Loading development environment (Rails 3.1.0)
ruby-1.9.2-p290 :001 > u = User.create({:starts_at => "2011-01-01 10:00"})
SQL (21.3ms)  INSERT INTO "users" ("created_at", "starts_at", "updated_at") VALUES (?, ?, ?)  [["created_at", Tue, 13 Dec 2011 11:32:50 CET +01:00], ["starts_at", Sat, 01 Jan 2011 10:00:00 CET +01:00], ["updated_at", Tue, 13 Dec 2011 11:32:50 CET +01:00]]
 => #<User id: 1, starts_at: "2011-01-01 09:00:00", created_at: "2011-12-13 10:32:50", updated_at: "2011-12-13 10:32:50"> 
ruby-1.9.2-p290 :002 > u.starts_at
 => Sat, 01 Jan 2011 10:00:00 CET +01:00 # datetime created
ruby-1.9.2-p290 :003 > u.starts_at = "2011-01-01 09:00:00" # new datetime with one hour back
 => "2011-01-01 09:00:00" 
ruby-1.9.2-p290 :004 > u.starts_at
 => Sat, 01 Jan 2011 09:00:00 CET +01:00 # changed datetime
ruby-1.9.2-p290 :005 > 
 => true 
ruby-1.9.2-p290 :006 > u.starts_at = "2011-01-01 09:00:00"
 => "2011-01-01 09:00:00" 
ruby-1.9.2-p290 :007 >
   (0.3ms)  UPDATE "users" SET "starts_at" = '2011-01-01 08:00:00.000000', "updated_at" = '2011-12-13 10:33:17.919092' WHERE "users"."id" = 1
 => true 

I've tested it in this fresh app, because I have a problem with this in larger application. What is going on? I've tried to browse the Rails code, tried to re-copy the relevant code 'by-hand' in console (like update, assign_attributes, even checked time_zone_conversion) and it worked, but not in 'real world'..


Had something similar

The problem appears to be here:

When rails it testing if the value was changed it compares old & new:

old = From cache (which is Time in your current timezone)
new = Time in UTC (+00:00) as saved in the database

If the difference in time is the UTC offset, the above erroneously succeeds (luckly the new cached value holds the intended change).

The next save/update compares with the new (and correct) cached value and marks the field as changed.

Appears like the fix should be:
old = old.in_time_zone if clone_with_time_zone_conversion_attribute?(attr, old)
old = old.in_time_zone(0) if clone_with_time_zone_conversion_attribute?(attr, old)

But I am yet to test the changes, so take this with a grain of salt.



I'm having the same issue in rails 3.2.1.

Can someone explain why the 'enhanced write method' in time_zone_conversion.rb:45 passes the original time to write_attribute (and thus to the dirty tracking), and not the time converted to the local time zone?:

write_attribute(:#{attr_name}, original_time)
@attributes_cache["#{attr_name}"] = time

this does not seem right.



Having the same issue on Rails 3.2.1.


A similar issue to this is here:

It was marked as resolved, but I'm still seeing the same behavior in 3.2.1.


I'm experiencing the same bug.

It's kind of awkward to tell customers they cannot change the time 1hr (or 2hrs, depending on daylight savings time). :)


Could someone create a test script that reproduces the problem?


I've written a test script, it's here: It gives the same results in 3.2.1 as in edge. I had to put in ActiveRecord::Base.time_zone_aware_attributes = true and ActiveRecord::Base.default_timezone = :utc in addition to the instructions in the article.





Also, when I change activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb:60 from:

write_attribute(:#{attr_name}, original_time)


write_attribute(:#{attr_name}, time)

It works as expected.


Confirmed that reproduces error.

@StefanH Are you going to write a test case and submit a pull request?


Yes I will look into it further. Never submitted a pull request before however, hope I do it right :). Any must-read articles on that before I try? (like


There is a screencast about it.


I've written a test to reproduce the problem, and an ugly solution:

It turns out that it is not as simple as changing write_attribute(:#{attr_name}, original_time) to write_attribute(:#{attr_name}, time), because that causes before_type_cast to fail. I've put some extra code in dirty.rb to handle time zone conversion (see gist). This fixes the problem, but it's bascally the same code that time_zone_conversion.rb:51 generates, so this is not very DRY.

I think the underlying problem is that the value that dirty.rb uses to determine if an attribute is dirty and the value that read_attribute returns eventually are not generated through the same code path. I think there is some duplication there (both in processing and in code).

Anyone have a better suggestion?

@lest lest added a commit to lest/rails that referenced this issue
@lest lest force datetime attributes to be changed, fix GH #3965 ddb5d2f

Is this still an issue?

Ruby on Rails member

Since #5196 was merged, and it says it fixes this, I'm closing.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Something went wrong with that request. Please try again.