It's About Time - Speaker Deck

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@AaronLasseigne 12 6 9 3 1 2 11 10 5 4 7 8 Time, Time Zones and Rails It’s About Time

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@AaronLasseigne Ruby

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@AaronLasseigne •Stores a year, month, and day. •Part of the standard library. require 'date' http://www.ruby-doc.org/stdlib-2.0/libdoc/date/rdoc/Date.html Date

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@AaronLasseigne •Stores a year, month, day, hour, minute, second, fraction of a second, and a UTC offset. •Part of the standard library. require 'date' http://www.ruby-doc.org/stdlib-2.0/libdoc/date/rdoc/DateTime.html DateTime

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@AaronLasseigne http://www.ruby-doc.org/core-2.0/Time.html •Stores a year, month, day, hour, minute, second, fraction of a second, and a UTC offset or a time zone (only local time or UTC). •Stored as the number of seconds since the Epoch, January 1, 1970 00:00 UTC. •Part of the Ruby core. Time

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@AaronLasseigne • Implemented in Ruby • Large Date Range • UTC Offset Support • Small API •Implemented in C (POSIX) •Limited Overall Date Range •UTC Offset Support •Limited Zone Support •Large API vs Time DateTime 1.8.7 Edition

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@AaronLasseigne Winner: Time

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@AaronLasseigne Time Offset vs Time Zone

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@AaronLasseigne Jan Feb Mar Apr May Jun July Aug Sept Oct Nov Dec “CST” – Central Standard Time (-6:00) “CDT” – Central Daylight Time (-5:00) Jan - Dec – “Central Time (US & Canada)”

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@AaronLasseigne DateTime doesn’t support time zones it supports offsets from UTC. Time offsets? irb> DateTime.new(2013, 1, 1, 0, 0, 0, 'CST').to_s # 'CST' or '-‐6:00' # => "2013-‐01-‐01T00:00:00-‐06:00" irb> DateTime.new(2013, 1, 1, 0, 0, 0, 'CDT').to_s # 'CDT' or '-‐5:00' # => "2013-‐01-‐01T00:00:00-‐05:00" irb> DateTime.new(2013, 1, 1, 0, 0, 0, 'Central Time (US & Canada)').to_s # => "2013-‐01-‐01T00:00:00+00:00"

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@AaronLasseigne Time doesn’t even support the abbreviated names. Time offsets? irb> Time.new(2013, 1, 1, 0, 0, 0, 'CST').to_s # => ArgumentError: "+HH:MM" or "-‐HH:MM" expected for utc_offset irb> Time.new(2013, 1, 1, 0, 0, 0, '-‐06:00').to_s # => "2013-‐01-‐01 00:00:00 -‐0600" irb> Time.new(2013, 1, 1, 0, 0, 0, '-‐05:00').to_s # => "2013-‐01-‐01 00:00:00 -‐0500"

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@AaronLasseigne Time offsets? irb> Time.new(2013, 1, 1, 0, 0, 0).to_s # => "2013-‐01-‐01 00:00:00 -‐0600" irb> Time.new(2013, 6, 1, 0, 0, 0).to_s # => "2013-‐06-‐01 00:00:00 -‐0500" irb> Time.utc(2013, 1, 1, 0, 0, 0).to_s # => "2013-‐01-‐01 00:00:00 UTC"

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@AaronLasseigne What is UTC?

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@AaronLasseigne “The primary time standard by which the world regulates clocks and time.[1]” •Formalized in 1963 by the International Radio Consultative Committee in Recommendation 374 •Based on UT1 and kept in sync with leap seconds. UTC 1. ^ Wikipedia “Coordinated Universal Time” Retrieved 29 August 2013

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@AaronLasseigne •Commonly denoted with a “z” or “Zulu”. •The “z” can also mean “zero”. UTC ± 00:00 irb> Time.parse('2012-‐1-‐1 12:00:00z') # => 2012-‐01-‐01 12:00:00 UTC

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@AaronLasseigne What does UTC stand for?

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@AaronLasseigne International Telecommunication Union and the International Astronomical Union

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@AaronLasseigne Coordinated Universal Time CUT

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@AaronLasseigne Temps Universel Coordonné TUC

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@AaronLasseigne Winner: UTC English: Universal Time Coordinated French: Universel Temps Coordonné

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@AaronLasseigne Rails

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@AaronLasseigne ActiveSupport

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@AaronLasseigne ActiveSupport::TimeZone

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@AaronLasseigne http://api.rubyonrails.org/classes/ActiveSupport/TimeZone.html ActiveSupport::TimeZone # application.rb: class Application < Rails::Application config.time_zone = 'Central Time (US & Canada)' end Time.zone # => # Time.zone.name # => "Central Time (US & Canada)" Time.zone.now # => Tue, 03 Sep 2013 19:00:00 CDT -‐05:00 Time.zone = 'Eastern Time (US & Canada)' Time.zone.now # => Tue, 03 Sep 2013 20:00:00 EDT -‐4:00

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@AaronLasseigne ActiveSupport::TimeWithZone

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@AaronLasseigne irb> Time.now.class # => Time < Object irb> Time.zone.class # => ActiveSupport::TimeZone < Object irb> Time.zone.now.class # => ActiveSupport::TimeWithZone < Object Let’s review!

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@AaronLasseigne Provides second, minute, hour, day, week, fortnight, month, and year. Time Using Numbers irb> 1.second # => 1 second irb> 1.minute # => 60 seconds irb> 1.month # => 2592000 seconds

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@AaronLasseigne •All have a plural version for better readability. •They work with Floats (except months and years). •All return seconds. Time Using Numbers

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@AaronLasseigne irb> 1.year.ago # => Mon, 03 Sep 2012 19:00:00 CDT -‐05:00 irb> 1.year.from_now # => Wed, 03 Sep 2014 19:00:00 CDT -‐05:00 Time From Numbers

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@AaronLasseigne irb> Time.days_in_month(6) # optional year argument # => 30 irb> Time.find_zone!('Eastern Time (US & Canada)') # => # irb> Time.use_zone('Eastern Time (US & Canada)') do Time.zone.now end # => Tue, 03 Sep 2013 20:00:00 EDT -‐4:00 Additions to Time

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@AaronLasseigne ActiveRecord

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@AaronLasseigne Database Mappings Migration MySQL PostgreSQL Ruby timestamp datetime timestamp without time zone TimeWithZone date date date Date time time time without time zone Time

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@AaronLasseigne •The date is set to Jan 1, 2000. •The time zone is set to UTC. How does a time ﬁeld become a Time?

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@AaronLasseigne rake time:zones:all Displays all time zones, also available: time:zones:us, time:zones:local -‐-‐ filter with OFFSET parameter, e.g., OFFSET=-‐6 rake -‐D time:zones:all term> What time zones are available?

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@AaronLasseigne term> rake time:zones:local * UTC -‐06:00 * Central America Central Time (US & Canada) Guadalajara Mexico City Monterrey Saskatchewan What time zones are available?

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@AaronLasseigne term> term> rake time:zones:us What time zones are available? * UTC -‐10:00 * Hawaii * UTC -‐09:00 * Alaska * UTC -‐08:00 * Pacific Time (US & Canada) * UTC -‐07:00 * Arizona ...

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@AaronLasseigne Adding Time Zones to Your Rails Project

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@AaronLasseigne 1 -‐> 2 -‐> 3 -‐> 4 -‐> 5 Conﬁgure an application time zone. # config/application.rb: class Application < Rails::Application ... config.time_zone = 'Central Time (US & Canada)' ... end

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@AaronLasseigne 1 -‐> 2 -‐> 3 -‐> 4 -‐> 5 Add a time zone ﬁeld to the user table. term> rails generate migration add_time_zone_to_users time_zone:string class AddTimeZoneToUsers < ActiveRecord::Migration def change add_column :users, :time_zone, :string end end

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@AaronLasseigne 1 -‐> 2 -‐> 3 -‐> 4 -‐> 5 Add a validation on the user model. # app/models/user.rb validates :time_zone, inclusion: {in: ActiveSupport::TimeZone.all.map(&:name)}

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@AaronLasseigne 1 -‐> 2 -‐> 3 -‐> 4 -‐> 5 Let the user select a time zone. # app/views/user_profile.html.erb <%= form.time_zone_select(:time_zone, ActiveSupport::TimeZone.us_zones) %>

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@AaronLasseigne 1 -‐> 2 -‐> 3 -‐> 4 -‐> 5 Use the time zone. # app/controllers/application_controller.rb around_filter :user_time_zone private def user_time_zone(&block) Time.use_zone(current_user.time_zone, &block) end

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@AaronLasseigne Gotchas and Best Practices

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@AaronLasseigne Date

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@AaronLasseigne Date.today

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@AaronLasseigne Date.today

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@AaronLasseigne Date.current

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@AaronLasseigne DateTime

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@AaronLasseigne Don’t use it.

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@AaronLasseigne Time

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@AaronLasseigne Don’t use it.

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@AaronLasseigne Don’t use it. * Some parts are acceptable (e.g. use_zone) *

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@AaronLasseigne Time.zone (ActiveSupport::TimeWithZone)

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@AaronLasseigne Time.now.utc is the same as Time.zone.now.utc

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@AaronLasseigne Time.now.utc is the same as Time.zone.now.utc

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@AaronLasseigne irb> ActiveSupport::TimeWithZone.name # => "Time" It Lies!

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@AaronLasseigne irb> t1 = Time.zone.now; t2 = Time.zone.now # => Tue, 03 Sep 2013 19:00:00 CDT -‐05:00 irb> t1 == t2 # => false irb> t1.usec # => 381876 irb> t2.usec # => 381911 Comparing Time

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@AaronLasseigne irb> t1 = Time.zone.now # => Tue, 03 Sep 2013 19:00:00 CDT -‐05:00 irb> t2 = t1.in_time_zone('Eastern Time (US & Canada)') # => Tue, 03 Sep 2013 20:00:00 EDT -‐04:00 irb> t1 == t2 # => true Comparing Time

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@AaronLasseigne irb> Time.zone.local(2013, 2, 1) + 1.year # => Sat, 01 Feb 2014 00:00:00 CST -‐06:00 irb> t = Time.zone.local(2016, 2, 1) # => Mon, 01 Feb 2016 00:00:00 CST -‐06:00 irb> t.leap_year? # => true irb> t + 1.year # => Wed, 01 Feb 2017 00:00:00 CST -‐06:00 Let’s do some math.

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@AaronLasseigne irb> 1.month / 1.day # => 30 irb> Time.zone.local(2013, 2, 1) + 1.month # => Fri, 01 Mar 2013 00:00:00 CST -‐06:00 irb> Time.zone.local(2013, 2, 1) + (1.year / 12) # => Sun, 03 Mar 2013 10:30:00 CST -‐06:00 irb> DateTime.new(2013, 2, 1) + (1.year / 12) # => Wed, 27 Mar 9213 00:00:00 +0000 Let’s do some math.

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@AaronLasseigne irb> t = Time.zone.local(2012, 6, 30).all_day # => Sat, 30 Jun 2012 00:00:00 CDT -‐05:00..Sat, 30 Jun 2012 23:59:59 CDT -‐05:00 irb> t.end.usec # => 999999 where(created_at: Time.zone.now.all_day) # => Records created that day relative to the user's time zone. Ranges

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@AaronLasseigne Testing

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@AaronLasseigne Timecop

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@AaronLasseigne # app/models/assignment.rb: def open? (available_at..due_at).cover?(Time.zone.now) end Assignment

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@AaronLasseigne # spec/models/assignment_spec.rb: describe '#open?' do context 'before the assignment is open' do it 'returns false' do Timecop.freeze(assignment.available_at -‐ 1.second) do expect(assignment.open?).to be_false end end end ... end Testing Assignment

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@AaronLasseigne # app/models/assignment.rb: scope :open, -‐> do where('available_at <= NOW() AND NOW() <= due_at') end Assignment

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@AaronLasseigne # app/models/assignment.rb: scope :open, -‐> do current_time = Time.zone.now where('available_at <= ? AND ? <= due_at', current_time, current_time) end Assignment

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@AaronLasseigne # spec/models/assignment_spec.rb: describe '.open' do subject(:assignment) { create(:assignment) } context 'before any assignments are open' do it 'returns no records' do Timecop.freeze(assignment.available_at -‐ 1.second) do expect(assignment.open).to have(0).records end end end ... end Testing Assignment

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@AaronLasseigne describe '#yada' do context 'before 1900' do before { Timecop.freeze(Time.zone.local(1899)) } after { Timecop.return } it '.....' {} it '.....' {} it '.....' {} end context 'after 1900' do ... end end DRY it up.

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@AaronLasseigne •Always use Time.zone. •Prefer Ruby/Rails over the database. •Test, test, test. Recap