Yet Another Time Zone Question


#1

Seems like there should be an easy solution to this problem, yet I
can’t seem to find one.

Here is the issue:
How do you assign a time zone to a Time object that results from a
parsed date/time string?

Example:

  • I receive a date time string from a date picker widget that does not
    include time zone info (i.e. “Mon May 11 18:24:37 2009”).
  • Time zone for this date is known and may be different than what’s
    local to the user
  • date/time is stored in the DB as unix time (i.e. 1242075962)
  • time zone is stored in the DB in tz format i(i.e. ‘America/
    New_York’)
  • I would like to be able to take a given date with its known time
    zone and calculate the equivalent unix time value.

now = Time.now
=> Mon May 11 18:24:37 -0400 2009

now.to_i
=> 1242080677

parsed = DateTime.parse(“Mon May 11 18:24:37 2009”)
=> Mon, 11 May 2009 18:24:37 +0000

parsed.to_time
=> Mon May 11 18:24:37 UTC 2009

parsed.to_time.to_i
=> 1242066277

Time.at 1242066277
=> Mon May 11 14:24:37 -0400 2009

It seems there should be a way to append the time zone to the string
before it is parsed or to associate the parsed time with a time zone
(without converting the time to the zone), however I can’t seem to
find an answer.

Any help would be greatly appreciated


#2

Hi,

The time zone is encoded in the string at the end e.g

Mon, 11 May 2009 18:24:37 +1200
Is in a time zone that’s +12 (12 hours ahead of utc)
DateTime.parse or Time.parse will read this correctly.

So what you’re doing is using a js date picker that gives you a string
like “Mon May 11 18:24:37 2009”
You just need to append the time zone difference to “Mon May 11
18:24:37 2009 +1200” etc before parsing.

I handle storing dates in the db a little differently than you, but if
you know what you’re doing don’t worry about changing that part.
I usually store dates in the db in utc format (I think you can
configure this in environment.rb from memory), and you can easily set
the user’s timezone in a filter in application controller
Time.zone = user.time_zone
which will handle all of the conversions for you.

Cheers,
Jeremy


#3

Thanks Jeremy!


#4

On Tue, May 12, 2009 at 6:31 PM, Jeremy Olliver
removed_email_address@domain.invalid wrote:

include time zone info (i.e. “Mon May 11 18:24:37 2009”).

  • Time zone for this date is known and may be different than what’s
    local to the user
  • date/time is stored in the DB as unix time (i.e. 1242075962)
  • time zone is stored in the DB in tz format i(i.e. ‘America/
    New_York’)
  • I would like to be able to take a given date with its known time
    zone and calculate the equivalent unix time value.

It seems there should be a way to append the time zone to the string
before it is parsed or to associate the parsed time with a time zone
(without converting the time to the zone), however I can’t seem to
find an answer.

The time zone is encoded in the string at the end e.g

Mon, 11 May 2009 18:24:37 +1200
Is in a time zone that’s +12 (12 hours ahead of utc)
DateTime.parse or Time.parse will read this correctly.

So what you’re doing is using a js date picker that gives you a string
like “Mon May 11 18:24:37 2009”
You just need to append the time zone difference to “Mon May 11
18:24:37 2009 +1200” etc before parsing.

Careful here, there’s a diference between a time zone like
“America/New_York” and a time zone offset
http://www.w3.org/TR/timezone/

I handle storing dates in the db a little differently than you, but if
you know what you’re doing don’t worry about changing that part.
I usually store dates in the db in utc format (I think you can
configure this in environment.rb from memory), and you can easily set
the user’s timezone in a filter in application controller
Time.zone = user.time_zone
which will handle all of the conversions for you.

Or to convert to an arbitrary timezone

Time.at(unix_time).in_timezone('America/New_York")


Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Twitter: http://twitter.com/RickDeNatale
WWR: http://www.workingwithrails.com/person/9021-rick-denatale
LinkedIn: http://www.linkedin.com/in/rickdenatale