Question

I want date part from an instance of ActiveSupport::TimeWithZone. I used to_date function for that but it returns date one day earlier.

For example, if datetime is 2012-04-11 09:05:00 UTC, and if I call to_date then it returns 2012-04-10 but 2012-04-11.

Also I am not using specific timezone (defaults to UTC)

The application is running on Ruby 1.8.7 and Rails 3.0.2

Can anyone please tell me why it gives wrong date? Also please suggest me if there is better way to get date (instance of Date) part from given DateTime (instance of ActiveSupport::TimeWithZone)

EDIT :
someone is also facing same issue here http://pastebin.com/sn8ExZiQ

NOTE : Time.zone returns 'UTC'

Answer 1

Thanks Jignesh. Here I am sharing your findings and solutions.

There may be some gem that is overriding to_date implementation and it may be implemented incorrectly and this overridden version might be getting called.

In my case the culprit was ruby-units gem

Root Cause : ruby-units gem included in the application’s Gemfile

Problem Analysis :

Gemfile

# Ruby-units overrides String class #to method, hence placed before Rails
gem "ruby-units" # Loads first and then rails is loaded

gem "rails", "3.0.11"

..
..

time.rb file (ruby-units gem codebase)

..
..

unless Time.instance_methods.include?(:to_date)
    # :nocov_19:
    # @return [Date]
    def to_date
     x=(Date.civil(1970,1,1)+((self.to_f+self.gmt_offset)/86400.0)-0.5)
     Date.civil(x.year, x.month, x.day)
    end
    # :nocov_19:
end

..
..

Lets say that current time in UTC time-zone is
Wed, 11 Apr 2012 10:12:17 UTC +00:00 represented by a ActiveSupport::TimeWithZone
instance.
From the rails application when we execute <TimeWithZone>.to_date it returns
a date 2012-04-10 which is incorrect.

The culprit involved in above incorrect behavior is the implementation of to_date method
provided by ruby-units gem

Below is a sample program to demonstrate the above incorrect behaviour. The to_date method is identical to one implemented by ruby-units gem, except that an argument is added to the method namely date_time and the self in the implementation is replaced by the argument
‘date_time’.

Sample Ruby Program to confirm the findings above:

require 'rubygems'
require 'active_support/all'

class TestDT
 def to_date(date_time)
     #x=(Date.civil(1970,1,1)+((self.to_f+self.gmt_offset)/86400.0)-0.5)
     x=(Date.civil(1970,1,1)+((date_time.to_f+date_time.gmt_offset)/86400.0)-0.5)
     Date.civil(x.year, x.month, x.day)
 end
end

tdt = TestDT.new
utc_time = Time.now.in_time_zone('UTC')
puts tdt.to_date(utc_time)

Output (date at the time of writing this was Wed, 11 Apr 2012 08:35:12 UTC +00:00):

$ ruby test_date_time.rb
2012-04-10

Solution:

1. Remove the ruby-units gem from the Gemfile or load it after rails gem
2. Workaround: Instead of executing datetime.to_date , use datetime.to_s.to_date