Ruby Get Time in Given Timezone

How to convert time with timezone in ruby

There's no method for that, however you can make one for yourself:

class Time
  require 'time'
  def self.by_offset(offset)
    at(now + zone_offset(offset))
  end
end

Now, you can:

Time.by_offset('PST')
#=> 2014-11-03 10:11:14 +0530
Time.now
#=> 2014-11-03 18:11:13 +0530

Tested with 1.9.2, 2.0.0, and 2.1.2 Rubies(MRI).

Create a Time object from a timezone and date and time?

Just use in_time_zone to parse the date in Time zone. You can pass Time zone as param.

in_time_zone(zone = ::Time.zone)

This will return exactly what you want.

'2016-12-25 12:00'.in_time_zone('America/Chicago')
#=> Sun, 25 Dec 2016 12:00:00 CST -06:00

'2016-12-25 12:00'.in_time_zone('America/New_York')
#=> Sun, 25 Dec 2016 12:00:00 EST -05:00

Rails 3: How to get today's date in specific timezone?

You should be able to do this: Time.current. That would display the current time in Melbourne if that's what Time.zone is set to.

Get Time Object at Start of Day in a Particular Time Zone

I ended up using the #local method on the ActiveSupport::TimeZone object passing components of the Date object.

# Get example date and time zone...
date = Date.today
timezone = ActiveSupport::TimeZone['America/New_York']

# Get beginning of day for date in timezone
timezone.local(date.year, date.month, date.day)

Get UTC offset for Timezone at given date via Ruby/tzinfo?

You can use the period_for_local method. For these examples, I'm using the timezone I live in (America/Sao_Paulo), in where the offset is -03:00 during winter (March to October) and -02:00 during summer (Daylight Saving Time):

# Sao Paulo timezone
zone = TZInfo::Timezone.new('America/Sao_Paulo')

# date in January (Brazilia Summer Time - DST)
d = DateTime.new(2017, 1, 1, 10, 0)

period = zone.period_for_local(d)
puts period.offset.utc_total_offset / 3600.0

# date in July (Brazilia Standard Time - not in DST)
d = DateTime.new(2017, 7, 1, 10, 0)

period = zone.period_for_local(d)
puts period.offset.utc_total_offset / 3600.0

The output is:

-2.0

-3.0

The utc_total_offset method returns the offset in seconds, so I divided by 3600 to get the value in hours.

Note that I also used 3600.0 to force the results to be a float. If I just use 3600, the results will be rounded and timezones like Asia/Kolkata (which has an offset of +05:30) will give incorrect results (5 instead of 5.5).

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Note that you must be aware of DST changes, because you can have either a gap or a overlap.

In São Paulo timezone, DST starts at October 15th 2017: at midnight, clocks shift forward to 1 AM (and offset changes from -03:00 to -02:00), so all the local times between 00:00 and 01:00 are not valid. In this case, if you try to get the offset, it will get a PeriodNotFound error:

# DST starts at October 15th, clocks shift from midnight to 1 AM
d = DateTime.new(2017, 10, 15, 0, 30)
period = zone.period_for_local(d) # error: TZInfo::PeriodNotFound

When DST ends, at February 18th 2018, at midnight clocks shift back to 11 PM of 17th (and offset changes from -02:00 to -03:00), so the local times between 11 PM and midnight exist twice (in both offsets).

In this case, you must specify which one you want (by setting the second parameter of period_for_local), indicating if you want the offset for DST or not:

# DST ends at February 18th, clocks shift from midnight to 11 PM of 17th
d = DateTime.new(2018, 2, 17, 23, 30)
period = zone.period_for_local(d, true) # get DST offset
puts period.offset.utc_total_offset / 3600.0 # -2.0

period = zone.period_for_local(d, false) # get non-DST offset
puts period.offset.utc_total_offset / 3600.0 # -3.0

If you don't specify the second parameter, you'll get a TZInfo::AmbiguousTime error:

# error: TZInfo::AmbiguousTime (local time exists twice due do DST overlap)
period = zone.period_for_local(d)

How do I.. get a value for time at 9:00am local, regardless of the timezone?

Ruby has a time class which maps to a time class in most databases. In most databases including mysql, it is represented as HH:mm:ss so the date portion is ignored.

The time should always remain the same (09:00) unless it is changed externally. You could fetch this time components using t.hour, and t.min, and construct a Date object with the correct date/time and the adjust for the users timezone.

>> t = Time.parse("09:00")
=> 2010-04-07 09:00:00 -0700
>> t.hour
=> 9
>> t.min
=> 0

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