Ruby / Rails - Change the timezone of a Time, without changing the value .
また、私が観察したいくつかの特異点を文書化しました。また、これらのヘルパーには、Rails フレームワークですぐに使用できない時間変換中に適用される自動夏時間調整を完全に無視するメソッドが含まれています。
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
上記のメソッドをクラスまたはモジュールにラップした後、Rails コンソールまたは Ruby スクリプトで試すことができる例:
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
お役に立てれば。