Question

The user inputs a date range let’s say from yesterday with any timezone.

from_datetime = "10/01/2012 00:00 +0545"

I get purchased time for the book like below:

purchased_at = Book.where("created_at > #{from_date}").purchased_at
=> Fri, 08 Jun 2012 09:44:26 UTC +00:00

The problem is this gives me UTC time but I want to show the purchased_at time in the requested time_zone which can vary.

I can’t use in_time_zone as the input from_date only has time offset, can I ?

purchased_at.in_time_zone("Kathmandu")
=> Fri, 08 Jun 2012 15:29:26 NPT +05:45

Is there any way around?

Answer 1

Give an offset, you can get a timezone name from ActiveSupport::TimeZone:

> ActiveSupport::TimeZone[5.hours + 45.minutes]
=> (GMT+05:45) Kathmandu

Then you can hand that to in_time_zone:

> Time.now.in_time_zone(ActiveSupport::TimeZone[5.hours + 45.minutes])
=> Thu, 18 Oct 2012 12:33:12 NPT +05:45 

You can pull the offset out of the from_datetime with a bit of simple wrangling if you know the incoming format.

There are issues with this approach:

1. The mapping from offset to name isn’t unique.
2. DST could be a problem if ActiveSupport::TimeZone[] gives you the wrong name.

Depending on your needs, you could just apply the offset manually and ignore the timezone when formatting the timestamp:

> (Time.now.utc + 5.hours + 45.minutes).strftime('%Y-%m-%d %H:%M:%S +0545')
=> "2012-10-18 12:40:12 +0545"