converting Date object to TimeWithZone

Question

I need to convert a Date object into a TimeWithZone object representing the beginning of that day in a given time zone.

The following approach works, but seems too convoluted as it requires me to convert the date to a string:

?> date = Date.parse("2010-02-17")
=> Wed, 17 Feb 2010
>> ActiveSupport::TimeZone['Eastern Time (US & Canada)'].parse(date.to_s)
=> Wed, 17 Feb 2010 00:00:00 EST -05:00
>> ActiveSupport::TimeZone['UTC'].parse(date.to_s)
=> Wed, 17 Feb 2010 00:00:00 UTC 00:00

Is there a better way I'm missing?

Edit: People are suggesting variations of:

?> date.to_datetime.in_time_zone('Eastern Time (US & Canada)').beginning_of_day
=> Tue, 16 Feb 2010 00:00:00 EST -05:00

As you can see, this isn't an equivalent conversion since it leaves me at the start of Feb. 16th EST, instead of the start of Feb. 17th EST.

Answer 1

I'm late to the party, but this is still a great question. ActiveSupport's in_time_zone was introduced since the O.P., but it does exactly what you want without parsing a string (slow) or setting Time.zone (risky):

>> date = Date.parse("2010-02-17")
=> Wed, 17 Feb 2010
>> date.in_time_zone('Eastern Time (US & Canada)')
=> Wed, 17 Feb 2010 00:00:00 EST -05:00

Of course if you want the beginning of day expressed at utc, you can do this:

>> date.in_time_zone('Eastern Time (US & Canada)').utc
=> 2010-02-17 05:00:00 UTC

Answer 2

If you have Time.zone set in Rails then you can call Date#at_beginning_of_day (see http://api.rubyonrails.org/classes/Date.html#method-i-at_beginning_of_day). Contrast this with Date#to_datetime:

Time.zone
 => #<ActiveSupport::TimeZone:0x10cf10858 @tzinfo=#<TZInfo::TimezoneProxy: Etc/UTC>, @utc_offset=nil, @current_period=nil, @name="UTC"> 

date = Date.today
 => Thu, 31 May 2012 

date.to_datetime
 => Thu, 31 May 2012 00:00:00 +0000 

date.at_beginning_of_day
 => Thu, 31 May 2012 00:00:00 UTC +00:00 

Time.zone = 'America/Chicago'
 => "America/Chicago" 

date.to_datetime
 => Thu, 31 May 2012 00:00:00 +0000 

date.at_beginning_of_day
 => Thu, 31 May 2012 00:00:00 CDT -05:00