Elegantly use multiple different time methods additively? - ruby-on-rails

Is there a way to use multiple time methods in an additive way?
Example: if the desired result was the time 3 weeks and 2 days ago, is there anything like this?
3.weeks.and.2.days.ago
I also tried
3.weeks.2.days.ago
What's the most elegant/sensible way to do this?
The best way I could come up with was
(3 + 2/7.to_d).weeks.ago
or
23.days.ago
But is there a way to use multiple time methods (e.g. weeks, days, hours etc) in the same command to make it easier to read?

ActiveSupport::Duration does not have a and method or any other method defined that works like that.
But want you can do ist this:
(3.weeks + 2.days).ago
#=> 2021-02-12 11:06:40.087082 +0100

There's also advance which returns a new date / time object based on the given options:
Time.current
#=> Sun, 07 Mar 2021 12:14:29 CET +01:00
Time.current.advance(weeks: -3, days: -2)
#=> Fri, 12 Feb 2021 12:14:29 CET +01:00
Options are :years, :months, :weeks, :days, :hours, :minutes, and :seconds.

Related

Is there an elegant way to use the app timezone when running a Rails ActiveRecord aggregate method?

When I use an ActiveRecord object's time field or use pluck on that field, I always (correctly) get back the time in the application's timezone:
> ClaritySurveyData::SurveyResponse.order(:id).first.submitted_at
=> Mon, 17 Sep 2012 09:46:33 PDT -07:00
> ClaritySurveyData::SurveyResponse.order(:id).pluck(:submitted_at).first
=> Mon, 17 Sep 2012 09:46:33 PDT -07:00
However, when a use an ActiveRecord aggregate method on the same field, I (incorrectly) get back the time in UTC:
> ClaritySurveyData::SurveyResponse.minimum(:submitted_at)
=> 2012-09-17 16:46:33 UTC
This bug has been biting me every few years, just infrequently enough that every time I have to figure it out afresh.
Obviously, I can easily work around it in specific cases using .in_time_zone.
However, I'd love to be able to patch it generally, so I don't ever have to figure it out again.
Any suggestions?

Given a timestamp, how to determine how many weeks ago?

I'm looking to return the number of weeks since a user was created in my app..
My model is User.rb (id, created_at)
Given user.created_at:
2.4.0 :008 > user.created_at
=> Mon, 14 Aug 2017 15:51:23 UTC +00:00
How can I do something like: user.created_at.weeks_ago where it returns some integer which represents the number of weeks since the user was created?
If you just want to build a human-friendly string, I believe time_ago_in_words is what you are after.
https://apidock.com/rails/ActionView/Helpers/DateHelper/time_ago_in_words
Otherwise, I would resort to something like the following:
(Time.new - user.created_at) / 1.week
If you want a more elegant solution, Subtract dates in Ruby and get the difference in minutes mentions the Time Difference gem for Ruby.
e.g.
TimeDifference.between(user.created_at.to_time, Time.now).in_weeks
I would use:
Time.current
=> Wed, 20 Sep 2017 03:56:15 UTC +00:00
Then
((Time.current - person.created_at)/604800).to_i
the subtraction gives you the number of seconds then divide it by 604800 which is the number of seconds in a week.

Daylight Saving Time start and end dates in Ruby/Rails

I'm working on a Rails app where I need to find the Daylight Saving Time start and end dates given a specific offset or timezone.
I basically save in my database the timezone offset received from a user's browser( "+3", "-5") and I want to modify it when it changes because of daylight saving time.
I know Time instance variables have the dst? and isdst methods which return true or false if the date stored in them is in the daylight saving time or not.
> Time.new.isdst
=> true
But using this to find the Daylight Saving Time beginning and end dates would take too many resources and I also have to do it for each timezone offset I have.
I would like to know a better way of doing this.
Ok, building on what you've said and #dhouty's answer:
You want to be able to feed in an offset and get a set of dates for knowing if there is a DST offset or not. I would recommend ending up with a range made of two DateTime objects, as that is easily used for many purposes in Rails...
require 'tzinfo'
def make_dst_range(offset)
if dst_end = ActiveSupport::TimeZone[offset].tzinfo.current_period.local_end
dst_start = ActiveSupport::TimeZone[offset].tzinfo.current_period.local_start
dst_range = dst_start..dst_end
else
dst_range = nil
end
end
Now you have a method that can do more than just take an offset thanks to the sugar that comes with ActiveSupport. You can do things like:
make_dst_range(-8)
#=> Sun, 08 Mar 2015 03:00:00 +0000..Sun, 01 Nov 2015 02:00:00 +0000
make_dst_range('America/Detroit')
#=> Sun, 08 Mar 2015 03:00:00 +0000..Sun, 01 Nov 2015 02:00:00 +0000
make_dst_range('America/Phoenix')
#=> nil #returns nil because Phoenix does not observe DST
my_range = make_dst_range(-8)
#=> Sun, 08 Mar 2015 03:00:00 +0000..Sun, 01 Nov 2015 02:00:00 +0000
Today happens to be August 29th so:
my_range.cover?(Date.today)
#=> true
my_range.cover?(Date.today + 70)
#=> false
my_range.first
#=> Sun, 08 Mar 2015 03:00:00 +0000
#note that this is a DateTime object. If you want to print it use:
my_range.first.to_s
#=> "2015-03-08T03:00:00+00:00"
my_range.last.to_s
#=> "2015-11-01T02:00:00+00:00"
ActiveSupport gives you all sorts of goodies for display:
my_range.first.to_formatted_s(:short)
#=> "08 Mar 03:00"
my_range.first.to_formatted_s(:long)
#=> "March 08, 2015 03:00"
my_range.first.strftime('%B %d %Y')
#=> "March 08 2015"
As you can see it's completely doable with just the offset, but as I said, offset doesn't tell you everything, so you might want to grab their actual time zone and store that as a string since the method will happily accept that string and still give you the date range. Even if you are just getting the time offset between your zone and theirs, you can easily figure correct that to the UTC offset:
my_offset = -8
their_offset = -3
utc_offset = my_offset + their_offset
What you are probably looking for is TZInfo::TimezonePeriod. Specifically, the methods local_start/utc_start and local_end/utc_end.
Given a timezone offset, you can get a TZInfo::TimezonePeriod object with
ActiveSupport::TimeZone[-8].tzinfo.current_period
Or if you have a timezone name, you can also get a TZInfo::TimezonePeriod object with
ActiveSupport::TimeZone['America/Los_Angeles'].tzinfo.current_period

Create a DateTime for tomorrow Ruby

I know I can create Date.tomorrow and there are options like midnight, at_noon etc. I need a more specific time than this.
Specifically, I am looking to create a DateTime that is tomorrow at 11am. I don't see anything in the DateTime docs. Is there any simple way to accomplish this? Thanks!
In Rails you would probably use tomorrow, in_time_zone and change:
Date.tomorrow.in_time_zone.change(hour: 11)
#=> Sat, 08 Aug 2015 11:00:00 CEST +02:00
This returns a ActiveSupport::TimeWithZone instance, just like midnight, at_noon etc.
Pure Ruby:
(Date.today + 1).to_datetime + Rational(11, 24)
or equivalently,
Date.today.to_datetime + Rational(35, 24)

Why does this rails query behave differently depending on timezone?

I have a rails time-based query which has some odd timezone sensitive behaviour, even though as far as I know I'm using UTC. In a nutshell, these queries give different answers:
>> Model.find(:all,:conditions=>['created_at<=?',(Time.now-1.hours).gmtime]).length
=> 279
>> Model.find(:all,:conditions=>['created_at<=?',(Time.now-1.hours)]).length
=> 280
Where the DB actually does contain one model created in the last hour, and the total number of models is 280. So only the first query is correct.
However, in environment.rb I have:
config.time_zone = 'UTC'
The system time zone (as reported by 'date') is BST (which is GMT+1) - so somehow this winds up getting treated as UTC and breaking queries.
This is causing me all sorts of problems as I need to parameterise the query passing in different times to an action (which are then converted using Time.parse()), and even though I send in UTC times, this 'off by one hour' DST issue crops a lot. Even using '.gmtime()' doesn't always seem to fix it.
Obviously the difference is caused somehow by an implicit conversion somewhere resulting in BST being incorrectly treated as UTC, but why? Doesn't rails store the timestamps in UTC? Isn't the Time class timezone aware? I am using Rails 2.2.2
So what is going on here - and what is the safe way to program around it?
edit, some additional info to show what the DB and Time class are doing:
>> Model.find(:last).created_at
=> Tue, 11 Aug 2009 20:31:07 UTC +00:00
>> Time.now
=> Tue Aug 11 22:00:18 +0100 2009
>> Time.now.gmtime
=> Tue Aug 11 21:00:22 UTC 2009
The Time class isn't directly aware of your configured timezone. Rails 2.1 added a bunch of timezone support, but Time will still act upon your local timezone. This is why Time.now returns a BST time.
What you likely want is to interact with Time.zone. You can call methods on this like you would the Time class itself but it will return it in the specified time zone.
Time.zone.now # => Tue, 11 Aug 2009 21:31:45 UTC +00:00
Time.zone.parse("2:30 PM Aug 23, 2009") # => Sun, 23 Aug 2009 14:30:00 UTC +00:00
Another thing you have to be careful with is if you ever do queries on the database where you are comparing times, but sure to use the UTC time (even if you have a different time zone specified) because Rails always stores UTC in the database.
Item.all(:conditions => ["published_at <= ?", Time.now.utc])
Also, instead of Time.now-1.hour do 1.hour.ago. It is easier to read and Rails will automatically use the configured timezone.
The TimeZone you need to set is UK, this will automatically handle BST
Time.zone = 'UK'
Time.zone.now
=> Sun, 17 Oct 2010 02:09:54 BST +01:00
start_date_format = DateTime.strptime(#start_date, date_format)
start_date_format_with_hour =
DateTime.strptime((start_date_format.to_i + timezone_offset*60*60).to_s,'%s').strftime(date_format)
end_date_format = DateTime.strptime(#end_date, date_format)
end_date_format_with_hour = DateTime.strptime((end_date_format.to_i + timezone_offset*60*60).to_s,'%s').strftime(date_format)
#filters_date = "invoices.created_at >= ? AND invoices.created_at < ?", start_date_format_with_hour, end_date_format_with_hour

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