Daylight savings with ruby on rails

handling daylight saving, time zone and time with ruby on rails

Knowledge transfer from Surendran Sukumaran

1. Time zone select with daylight handling

On Fri, 12 Jun 2020 22:27:45

Daylight saving time in the United States 2020 in Colorado began on
Sunday,8 March and ends on Sunday,1 November

Daylight saving is skipped in time_zone_select

<%= form.time_zone_select :timezone, nil, { default: 'Chennai' }, { :class => "form-control", required: "required", id: 'match_timezone' } %>

With the help of formatted_offset

<%= form.select :timezone, ActiveSupport::TimeZone.all.sort_by(&:name).map{|e| ["#{e.name}(GMT#{e.now.formatted_offset})", e.name]}, { selected: 'Chennai' }, { :class => "form-control", required: "required", id: 'match_timezone' } %>

2. Building date time object with daylight

date = Date.strptime('06/18/2020', "%m/%d/%Y")
start_time = '07:00 AM'
Time.zone = "Pacific Time (US & Canada)"

with DateTime.parse

[205] pry(main)> DateTime.parse("#{date.year}-#{date.month}-#{date.day} #{start_time} #{Time.zone}")
=> Thu, 18 Jun 2020 07:00:00 -0800

with Time.zone.parse

[209] pry(main)> Time.zone.parse("#{date.year}-#{date.month}-#{date.day} #{start_time}")
=> Thu, 18 Jun 2020 07:00:00 PDT -07:00

3. Better code

a. method with Time.zone = “Pacific Time (US & Canada)”

recommended

def update
  Time.use_zone('Pacific Time (US & Canada)') do
    match_reminder_email
  end
end
def match_reminder_email
  date = Date.strptime('06/18/2020', "%m/%d/%Y")
  start_time = '07:00 AM'
  start_date = Time.zone.parse("#{date.year}-#{date.month}-#  {date.day} #{start_time}")
end

Not recommended

def update
  match_reminder_email
end
def match_reminder_email
  date = Date.strptime('06/18/2020', "%m/%d/%Y")
  start_time = '07:00 AM'
  Time.zone = "Pacific Time (US & Canada)"
  start_date = Time.zone.parse("#{date.year}-#{date.month}-#{date.day} #{start_time}")
end

b. Between Time.now and Time.current

The difference of .current and .now is .now use the server's timezone, while .current use what the Rails environment is set to. If it's not set, then .current will be same as .now.

[227] pry(main)> Time.now 
=> 2020-06-13 00:11:12 +0530

[229] pry(main)> Time.current
=> Fri, 12 Jun 2020 11:41:17 PDT -07:00

Reference
a. https://stackoverflow.com/questions/12748626/when-should-datetime-now-utc-vs-time-current-utc-be-used-in-rails

b. https://apidock.com/rails/DateTime/formatted_offset