I'm running into a wall. I want to get yesterday's time in milliseconds. I thought the below would do the job
irb(main):001:0> yday = 1.day.ago
=> Tue, 03 Apr 2018 20:35:24 UTC +00:00
irb(main):002:0> yday.strftime('%Q').to_f
=> 0.0
but as you can see I'm getting a "0.0" for yesterday's time. How can I correct what I have to accurately get the time in milliseconds?
You have two options:
(DateTime.now-1.day).strftime('%Q')
Or:
yday = 1.day.ago
yday.to_datetime.strftime('%Q')
Why you need to_datetime? Well, 1.day.ago is ActiveSupport::TimeWithZone which does not have %Q format (documentation) when strftime for DateTime does (documentation)
Related
There is task model with attributes when and duration.
create_table "tasks", force: true do |t|
...
t.datetime "when"
t.integer "duration"
...
end
I wrote method for checking if task is active so I can show it on page.
This is active method:
def active?
if (self.when + self.duration) > Time.now
true
end
end
I tried in console to inspect object:
t.when + t.duration
=> Sun, 08 Sep 2013 01:01:00 UTC +00:00
DateTime.now
=> Sun, 08 Sep 2013 01:57:13 +0200
t.active?
=> true
It's true but I entered 1:00 time and 1 minute for duration and I hoped it shouldn't be true.
It seems that when column in database is not saved in correct time zone, so it gives incorrect results. How to solve this issue?
It seems that when column in database is not saved in correct time zone
1) Rails automatically converts times to UTC time before inserting them in the database (which is a good thing), which means the times have an offset of "+0000" . That means if you save a time of 8pm to the database, and your server is located in a timezone with an offset of "+0600", then the equivalent UTC time is 2pm, so 2pm gets saved in the database. In other words, your local server's time is 6 hours ahead of UTC time, which means that when it's 8pm in your server's time zone, it's 2pm in the UTC timezone.
2) When you compare dates, ruby takes the timezone offset into account--in other words ruby converts all times to the same timezone and then compares the times. Here is an example:
2.0.0p247 :086 > x = DateTime.strptime('28-01-2013 08:00:00 PM +6', '%d-%m-%Y %I:%M:%S %p %z')
=> Mon, 28 Jan 2013 20:00:00 +0600
2.0.0p247 :087 > y = DateTime.strptime('28-01-2013 08:20:00 PM +7', '%d-%m-%Y %I:%M:%S %p %z')
=> Mon, 28 Jan 2013 20:20:00 +0700
2.0.0p247 :088 > x < y
=> false
If you just compare the times of the two Datetime objects, x is less than y. However, y has a time of 8:20pm in a timezone that has an offset of +7, which is equivalent to the time 7:20pm in a timezone with an offset of +6. Therefore, y is actually less than x. You need to compare apples to apples, which means you need to mentally compare times that have been converted to the same timezone to get the same results as ruby/rails produces.
3) You can convert Time.now to a UTC time using the rails utc() method:
2.0.0p247 :089 > x = Time.now
=> 2013-09-07 8:00:00 +0600
2.0.0p247 :090 > x.utc
=> 2013-09-07 02:00:00 UTC
That's what ruby does before comparing Time.now to task.when + task.duration
4) You might find it more convenient to create a DateTime object with the time you want using:
DateTime.strptime('28-01-2013 08:00:00 PM +0', '%d-%m-%Y %I:%M:%S %p %z'
Because you are able to specify the offset as zero, you don't have to create a time that anticipates the conversion to UTC time.
Or you can use the change() method, which causes the offset() to change without converting the time:
2.0.0p247 :011 > x = DateTime.now
=> Sun, 08 Sep 2013 00:34:08 +0600
2.0.0p247 :012 > x.change offset: "+0000"
=> Sun, 08 Sep 2013 00:34:08 +0000
ActiveRecord stores timestamps in UTC by default. See How to change default timezone for Active Record in Rails? for changing default time zone.
You can also just use Time#in_time_zone to convert t.when to your timezone, see http://api.rubyonrails.org/classes/ActiveSupport/TimeWithZone.html.
I am having problems with a query because midnight conversion is not working as expected.
time = Date.today.midnight #=> Mon, 15 Jul 2013 00:00:00 BRT -03:00
time.class #=> ActiveSupport::TimeWithZone
condition = Task.arel_table[:scheduled_to].gt(time)
condition.to_sql #=> "`tasks`.`scheduled_to` > '2013-07-15 03:00:00'"
I was expecting the generated sql to be
`tasks`.`scheduled_to` > '2013-07-15 00:00:00'"
My Time zone is GMT -3. If i change the time zone so it matches GMT -5 the generated sql is
condition.to_sql #=> "`tasks`.`scheduled_to` > '2013-07-15 05:00:00'"
Rails 4.0.0
Ruby 2.0.0p247
Is there any way to ignore the timezone so the query behaves like expected?
Timezones are relative to UTC (0000), so you gotta remove it from your Date.
DateTime.now.midnight.utc #=> '2013-08-23 03:00:00 +0000'
Now, just get rid from the compensated hours.
DateTime.now.midnight.utc.change({:hour => 0, :min => 0}) #=> '2013-08-23 00:00:00 +0000'
Not sure if there is a cleaner way to do it, but it worked for me (Ruby 1.9.3p385).
Date.current or Date.today.midnight.utc Should have solved the problem.
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,
)
I would expect Time and to_time to be reflective.
UPDATE
This is the answer, if you add the parameter :local, it doesn't ignore the offset. I find it wierd that it ignores data (the offset) by default, though...
Time.zone.now.to_s.to_time(:local) returns 2012-03-20 14:39:03 +0100
/UPDATE
> Time.zone.now.to_s
=> "2012-03-20 12:50:05 +0100"
> Time.zone.now.to_s.to_time.to_s
=> "2012-03-20 12:50:05 UTC"
# PROBLEM:
# UTC is +0000, meaning that there is 1 hour diff in the above
> Time.zone.now
=> Tue, 20 Mar 2012 12:51:32 CET +01:00
> Time.zone.now.to_time
=> Tue, 20 Mar 2012 12:51:32 CET +01:00
> Time.zone.now.to_json
=> "\"2012-03-20T12:50:36+01:00\""
> Time.zone.now.to_json.to_time
=> 2012-03-20 12:50:36 UTC
I have this problem with JSON messages. Anyway, I wouldn't expect to_time to actually change the time. OK to translate to UTC, probably, but it should adjust time accordingly. Anybody know if this is a known issue or "by design"?
This method, String#to_time, defined in ActiveSupport takes one parameter, form, which can be either :utc (default) or :local. So by default, it always returns a Time in UTC.
To get a Time with timezone:
Time.zone.parse("2012-03-20T12:50:36+01:00")
I have a DateTime object representing a particular date, as in "2011-01-15 00:00:00 UTC" to represent January 15th. I would like to produce the range of times in a particular time zone that have the same date.
The method signature would probably be something like
def day_range_for(date, tz)
# ...
end
For example, if I have range_for(DateTime.parse('2011-01-15'), 'CST'), then I want the result to be a range like 2011-01-15 00:00:00 -0600 .. 2011-01-15 23:59:59 -0600.
Can you take the input string instead of the object? If you pass in a DateTime object, its a tad counter intuitive because the time the object represents isn't the actual time you are looking for. It would conform to my expectations if you either passed in the correct, absolute DateTime, or the string itself. The actual meat of the problem is entirely handled by ActiveSupport, which I think you are using since you tagged this question with Rails. How does this look?
def range_for(input, tz=nil)
if tz.is_a?(String)
tz = ActiveSupport::TimeZone.new(tz)
else
tz = Time.zone
end
if input.acts_like?(:date) || input.acts_like?(:time)
d = input.in_time_zone(tz)
else
d = tz.parse(input)
end
return d.beginning_of_day..d.end_of_day
end
Have a look:
ruby-1.9.2-p0 > range_for('2011-01-15', 'Alaska')
=> Sat, 15 Jan 2011 00:00:00 AKST -09:00..Sat, 15 Jan 2011 23:59:59 AKST -09:00
ruby-1.9.2-p0 > range_for(Time.zone.now)
=> Mon, 10 Jan 2011 00:00:00 EST -05:00..Mon, 10 Jan 2011 23:59:59 EST -05:00
ruby-1.9.2-p0 > range_for('2011-01-15', 'EST')
=> Sat, 15 Jan 2011 00:00:00 EST -05:00..Sat, 15 Jan 2011 23:59:59 EST -05:00
How about:
def day_range_for date, zone
(DateTime.new(date.year,date.month,date.day,0,0,0,zone)..DateTime.new(date.year,date.month,date.day,23,59,59,zone))
end
day_range_for(DateTime.parse('2011-01-15'), 'CST')
#=> #<DateTime: 2011-01-15T00:00:00-06:00 (9822307/4,-1/4,2299161)>..#<DateTime: 2011-01-15T23:59:59-06:00 (212161917599/86400,-1/4,2299161)>