I'm trying to parse a timestamp from a string, and then subsequently display it with its abbreviated time zone, but what's coming back is the numeric offset from UTC despite what I believe is the correct usage. Here's the console session:
[5] pry(main)> time_string = "2022-08-02T12:00:00 CDT"
=> "2022-08-02T12:00:00 CDT"
[6] pry(main)> DateTime.parse(time_string).zone
=> "-05:00"
[7] pry(main)> DateTime.parse(time_string).strftime("%Z")
=> "-05:00"
What I'm expecting here is that this will return CDT again.
This is Ruby 2.7 on macOS, with Rails:
❯ ruby --version
ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-darwin21]
❯ rails --version
Rails 6.1.6
From the strftime docs for rails, says it's working as intended.
Time zone:
%z - Time zone as hour and minute offset from UTC (e.g. +0900)
%:z - hour and minute offset from UTC with a colon (e.g. +09:00)
%::z - hour, minute and second offset from UTC (e.g. +09:00:00)
%:::z - hour, minute and second offset from UTC
(e.g. +09, +09:30, +09:30:30)
%Z - Equivalent to %:z (e.g. +09:00)
If you have the actual timezone name you can use that to get the abbreviation as outline here in the blog post
def human_timezone(time_string, timezone)
time = time_string.in_time_zone(timezone)
if time.zone.match?(/^\w/)
time.zone
else
time.formatted_offset
end
end
>> human_timezone('2019-03-28 16:00', 'Pacific Time (US & Canada)')
=> "PDT"
>> human_timezone('2019-03-28 16:00', 'Berlin')
=> "CET"
>> human_timezone('2019-05-01 16:00', 'Almaty')
=> "+06:00"
Ruby doesn't store timezone name, it stores only the time offset (-5:00).
So, backward conversion is not possible because there are multiple timezones for one offset. For e.g. another timezone with -5:00 offset.
> time_string = "2022-08-02T12:00:00 PET"
=> "2022-08-02T12:00:00 PET"
> DateTime.parse time_string
=> Tue, 02 Aug 2022 12:00:00 -0500
I have a ruby on rails app that creates event, from the frontend the date of the event is generated in Mountain Time and then the application transforms it in UTC.
The issue is that since the events are generated in the future sometimes we have issues with the clock change.
Let's say the event should happen:
Day X at 9:30 MT
It would be transformed in:
Day X at 14:30 UTC
But if we create an event in the future that fall in the week the clock change we would have an event configured at the wrong time, because it does not take into consideration the clock change.
Is there a way to generate a UTC dateTime from a specific TimeZone considering if the clock change would happen in that date?
According to Rails API
if your app has its time zone configured as Mountain Time(MT),
Daylight Saving Time(DST) works by default
# application.rb:
class Application < Rails::Application
config.time_zone = 'Mountain Time (US & Canada)'
end
Time.zone # => #<ActiveSupport::TimeZone:0x000000...>
Time.zone.name # => "Mountain Time (US & Canada)"
Time.zone.now # => Tue, 14 Dec 2021 09:46:09 MST -07:00
So if the event date falls after
the DST change, parsing (see ActiveSupport::TimeWithZone)
that date should return the appropiate time
time = Time.zone.parse('2022-03-13 01:00:00') # the parsed datetime is in the same timezone
=> Sun, 13 Mar 2022 01:00:00 MST -07:00
time.dst?
=> false
time = Time.zone.parse('2022-03-13 02:00:00')
=> Sun, 13 Mar 2022 03:00:00 MDT -06:00
time.dst?
=> true
You mention that the application transforms it to UTC. So if I assume,
the correct UTC date is passed to the backend(maybe as an ISO8601 encoded string), you should parse it and convert it to the app time zone by doing something like this:
date = params[:date]
# => "2021-12-14 18:05:05"
utc_datetime = DateTime.parse(date, "%Y-%m-%d %H:%M:%S")
=> 2021-12-14 18:05:05 +0000
mt_datetime = utc_datetime.in_time_zone
=> 2021-12-14 11:05:05 MST -07:00
...
end
I am trying to parse a string that's hitting my api. The incoming string is
"2014-03-19T04:00:00.000Z"
I need it in the following format for my db sql to work:
"2014-03-19 00:00:00 -0400"
Right now, the solution I have come up with is
Time.zone.parse("2014-03-19T04:00:00.000Z").in_time_zone('America/New_York').to_s
This feels like an inelegant solution to me and I feel that there should be a more dynamic way of doing things without specifying the time zone name (it should be local by default). I just want to switch the formatting of the strings as they are supposed to be equivalent.
Thanks
Configure the time_zone in the application.rb file and use it as below:
# application.rb:
class Application < Rails::Application
config.time_zone = 'America/New_York'
end
Time.zone.parse("2014-03-19T04:00:00.000Z").to_s
# => "2014-03-19 00:00:00 -0400"
More examples of use
$ > Time.zone = "America/New_York"
# => "America/New_York"
$ > Time.zone
# => (GMT-05:00) America/New_York
$ > Time.zone.now
# => Sat, 22 Mar 2014 18:28:48 EDT -04:00
irb(main):008:0> Time.parse("2014-03-19T04:00:00.000Z").getlocal.strftime("%F %T %z")
=> "2014-03-19 04:00:00 +0000"
On a system in GMT+1:
irb(main):003:0> Time.parse("2014-03-19T04:00:00.000Z").getlocal.strftime("%F %T %z")
=> "2014-03-19 05:00:00 +0100"
I have a date stored in UTC in my Rails app and am trying to display it to a user who has "Eastern Time (US & Canada)" as their timezone. The problem is that rails keeps converting it to Eastern Daylight Time (EDT) so midnight is being displayed as 8am when it should be 7am. Is there anyway to prevent the DST conversion?
>> time = DateTime.parse("2013-08-26T00:00:00Z")
=> Mon, 26 Aug 2013 00:00:00 +0000
>> time.in_time_zone("Eastern Time (US & Canada)")
=> Sun, 25 Aug 2013 20:00:00 EDT -04:00
Update
I eventually went with a twist on #zeantsoi 's approach. I'm not a huge fan of adding too many rails helpers so I extended active support's TimeWithZone class.
class ActiveSupport::TimeWithZone
def no_dst
if self.dst?
self - 1.hour
else
self
end
end
end
Now I can do time.in_time_zone("Eastern Time (US & Canada)").no_dst
Create a helper that utilizes the dst? method on TimeZone to check whether the passed timezone is currently in DST. If it is, then subtract an hour from the supplied DateTime instance:
# helper function
module TimeConversion
def no_dst(datetime, timezone)
Time.zone = timezone
if Time.zone.now.dst?
return datetime - 1.hour
end
return datetime
end
end
Then, render the adjusted (or non-adjusted) time in your view:
# in your view
<%= no_dst(DateTime.parse("2013-08-26T00:00:00Z"), 'Eastern Time (US & Canada)') %>
#=> Sun, 25 Aug 2013 19:00:00 EDT -04:00
I have a record foo in the database which has :start_time and :timezone attributes.
The :start_time is a Time in UTC - 2001-01-01 14:20:00, for example.
The :timezone is a string - America/New_York, for example.
I want to create a new Time object with the value of :start_time but whose timezone is specified by :timezone. I do not want to load the :start_time and then convert to :timezone, because Rails will be clever and update the time from UTC to be consistent with that timezone.
Currently,
t = foo.start_time
=> 2000-01-01 14:20:00 UTC
t.zone
=> "UTC"
t.in_time_zone("America/New_York")
=> Sat, 01 Jan 2000 09:20:00 EST -05:00
Instead, I want to see
=> Sat, 01 Jan 2000 14:20:00 EST -05:00
ie. I want to do:
t
=> 2000-01-01 14:20:00 UTC
t.zone = "America/New_York"
=> "America/New_York"
t
=> 2000-01-01 14:20:00 EST
Sounds like you want something along the lines of
ActiveSupport::TimeZone.new('America/New_York').local_to_utc(t)
This says convert this local time (using the zone) to utc. If you have Time.zone set then you can of course to
Time.zone.local_to_utc(t)
This won't use the timezone attached to t - it assumes that it's local to the time zone you are converting from.
One edge case to guard against here is DST transitions: the local time you specify may not exist or may be ambiguous.
I've just faced the same problem and here is what I'm going to do:
t = t.asctime.in_time_zone("America/New_York")
Here is the documentation on asctime
If you're using Rails, here is another method along the lines of Eric Walsh's answer:
def set_in_timezone(time, zone)
Time.use_zone(zone) { time.to_datetime.change(offset: Time.zone.now.strftime("%z")) }
end
You need to add the time offset to your time after you convert it.
The easiest way to do this is:
t = Foo.start_time.in_time_zone("America/New_York")
t -= t.utc_offset
I am not sure why you would want to do this, though it is probably best to actually work with times the way they are built. I guess some background on why you need to shift time and timezones would be helpful.
Actually, I think you need to subtract the offset after you convert it, as in:
1.9.3p194 :042 > utc_time = Time.now.utc
=> 2013-05-29 16:37:36 UTC
1.9.3p194 :043 > local_time = utc_time.in_time_zone('America/New_York')
=> Wed, 29 May 2013 12:37:36 EDT -04:00
1.9.3p194 :044 > desired_time = local_time-local_time.utc_offset
=> Wed, 29 May 2013 16:37:36 EDT -04:00
Depends on where you are going to use this Time.
When your time is an attribute
If time is used as an attribute, you can use the same date_time_attribute gem:
class Task
include DateTimeAttribute
date_time_attribute :due_at
end
task = Task.new
task.due_at_time_zone = 'Moscow'
task.due_at # => Mon, 03 Feb 2013 22:00:00 MSK +04:00
task.due_at_time_zone = 'London'
task.due_at # => Mon, 03 Feb 2013 22:00:00 GMT +00:00
When you set a separate variable
Use the same date_time_attribute gem:
my_date_time = DateTimeAttribute::Container.new(Time.zone.now)
my_date_time.date_time # => 2001-02-03 22:00:00 KRAT +0700
my_date_time.time_zone = 'Moscow'
my_date_time.date_time # => 2001-02-03 22:00:00 MSK +0400
Here's another version that worked better for me than the current answers:
now = Time.now
# => 2020-04-15 12:07:10 +0200
now.strftime("%F %T.%N").in_time_zone("Europe/London")
# => Wed, 15 Apr 2020 12:07:10 BST +01:00
It carries over nanoseconds using "%N". If you desire another precision, see this strftime reference.
The question's about Rails but it seems, like me, not everyone here is on the ActiveSupport train, so yet another option:
irb(main):001:0> require "time"
=> true
irb(main):003:0> require "tzinfo"
=> true
irb(main):004:0> t = Time.parse("2000-01-01 14:20:00 UTC")
=> 2000-01-01 14:20:00 UTC
irb(main):005:0> tz = TZInfo::Timezone.get("America/New_York")
=> #<TZInfo::DataTimezone: America/New_York>
irb(main):008:0> utc = tz.local_to_utc(t)
=> 2000-01-01 19:20:00 UTC
irb(main):009:0> tz.utc_to_local(utc)
=> 2000-01-01 14:20:00 -0500
irb(main):010:0>
local_to_utc not doing the opposite of utc_to_local might look like a bug but it is at least documented: https://github.com/tzinfo/tzinfo says:
The offset of the time is ignored - it is treated as if it were a local time for the time zone
I managed to do this by calling change with the desired time zone:
>> t = Time.current.in_time_zone('America/New_York')
=> Mon, 08 Aug 2022 12:04:36.934007000 EDT -04:00
>> t.change(zone: 'Etc/UTC')
=> Mon, 08 Aug 2022 12:04:36.934007000 UTC +00:00
https://api.rubyonrails.org/classes/ActiveSupport/TimeWithZone.html#method-i-change
def relative_time_in_time_zone(time, zone)
DateTime.parse(time.strftime("%d %b %Y %H:%M:%S #{time.in_time_zone(zone).formatted_offset}"))
end
Quick little function I came up with to solve the job. If someone has a more efficient way of doing this please post it!
I spent significant time struggling with TimeZones as well, and after tinkering with Ruby 1.9.3 realized that you don't need to convert to a named timezone symbol before converting:
my_time = Time.now
west_coast_time = my_time.in_time_zone(-8) # Pacific Standard Time
east_coast_time = my_time.in_time_zone(-5) # Eastern Standard Time
What this implies is that you can focus on getting the appropriate time setup first in the region you want, the way you would think about it (at least in my head I partition it this way), and then convert at the end to the zone you want to verify your business logic with.
This also works for Ruby 2.3.1.
I have created few helper methods one of which just does the same thing as is asked by the original author of the post at Ruby / Rails - Change the timezone of a Time, without changing the value.
Also I have documented few peculiarities I observed and also these helpers contains methods to completely ignore automatic day-light savings applicable while time-conversions which is not available out-of-the-box in Rails framework:
def utc_offset_of_given_time(time, ignore_dst: false)
# Correcting the utc_offset below
utc_offset = time.utc_offset
if !!ignore_dst && time.dst?
utc_offset_ignoring_dst = utc_offset - 3600 # 3600 seconds = 1 hour
utc_offset = utc_offset_ignoring_dst
end
utc_offset
end
def utc_offset_of_given_time_ignoring_dst(time)
utc_offset_of_given_time(time, ignore_dst: true)
end
def change_offset_in_given_time_to_given_utc_offset(time, utc_offset)
formatted_utc_offset = ActiveSupport::TimeZone.seconds_to_utc_offset(utc_offset, false)
# change method accepts :offset option only on DateTime instances.
# and also offset option works only when given formatted utc_offset
# like -0500. If giving it number of seconds like -18000 it is not
# taken into account. This is not mentioned clearly in the documentation
# , though.
# Hence the conversion to DateTime instance first using to_datetime.
datetime_with_changed_offset = time.to_datetime.change(offset: formatted_utc_offset)
Time.parse(datetime_with_changed_offset.to_s)
end
def ignore_dst_in_given_time(time)
return time unless time.dst?
utc_offset = time.utc_offset
if utc_offset < 0
dst_ignored_time = time - 1.hour
elsif utc_offset > 0
dst_ignored_time = time + 1.hour
end
utc_offset_ignoring_dst = utc_offset_of_given_time_ignoring_dst(time)
dst_ignored_time_with_corrected_offset =
change_offset_in_given_time_to_given_utc_offset(dst_ignored_time, utc_offset_ignoring_dst)
# A special case for time in timezones observing DST and which are
# ahead of UTC. For e.g. Tehran city whose timezone is Iran Standard Time
# and which observes DST and which is UTC +03:30. But when DST is active
# it becomes UTC +04:30. Thus when a IRDT (Iran Daylight Saving Time)
# is given to this method say '05-04-2016 4:00pm' then this will convert
# it to '05-04-2016 5:00pm' and update its offset to +0330 which is incorrect.
# The updated UTC offset is correct but the hour should retain as 4.
if utc_offset > 0
dst_ignored_time_with_corrected_offset -= 1.hour
end
dst_ignored_time_with_corrected_offset
end
Examples which can be tried on rails console or a ruby script after wrapping the above methods in a class or module:
dd1 = '05-04-2016 4:00pm'
dd2 = '07-11-2016 4:00pm'
utc_zone = ActiveSupport::TimeZone['UTC']
est_zone = ActiveSupport::TimeZone['Eastern Time (US & Canada)']
tehran_zone = ActiveSupport::TimeZone['Tehran']
utc_dd1 = utc_zone.parse(dd1)
est_dd1 = est_zone.parse(dd1)
tehran_dd1 = tehran_zone.parse(dd1)
utc_dd1.dst?
est_dd1.dst?
tehran_dd1.dst?
ignore_dst = true
utc_to_est_time = utc_dd1.in_time_zone(est_zone.name)
if utc_to_est_time.dst? && !!ignore_dst
utc_to_est_time = ignore_dst_in_given_time(utc_to_est_time)
end
puts utc_to_est_time
Hope this helps.
This worked well for me
date = '23/11/2020'
time = '08:00'
h, m = time.split(':')
timezone = 'Europe/London'
date.to_datetime.in_time_zone(timezone).change(hour: h, min: m)
This changes the timezone to 'EST' without changing the time:
time = DateTime.current
Time.find_zone("EST").local(
time.year,
time.month,
time.day,
time.hour,
time.min,
time.sec,
)