for a while I´m trying to understand how this timezone times will work, and I had a question:
Today in my country, we are in Daylight saving time (GMT-2).
So the user of my application enter a time, like 11:00AM and post the form.
Far as I know, rails will convert this date to UTC and save in the database (mysql in my case), like: 01:00PM UTC.
When I recover that record, I had to convert to local time to display. Ok?
My question is, lets suppose that this date/time represents a date/time in future, when my country gets out from summer time (GMT-3). Rails will save 01:00PM UTC? Today, in Daylight saving time, how will be the local time? And in the future, how will be this local time?
Basically, I always need to display to user 11:00AM.
thanks.
There are several places where timezone can come into play: the operating system (or probably user account) default setting, the database server, Rails environment.rb.
The key is to make sure all dates are stored with UTC time zone, then displayed in whatever your local timezone is. It sounds like you're doing that.
So your question seems to boil down to "if it's Daylight time, I want to offset by -3 hours, else offset by -2 hours". The Rails time extensions let you determine your current offset like Time.zone.now.utc_offset, and Time#dst? tells you if it's Daylight Savings Time with those two you can conditionally subtract the extra hour (3600 hundred seconds).
7 months after you asked, but perhaps skip_time_zone_conversion_for_attributes= will help - it tells AcitveRecord not to convert timezones on storage or retrieval. See ActiveRecord Timestamp which shows the example:
class Topic < ActiveRecord::Base
self.skip_time_zone_conversion_for_attributes = [:written_on]
end
Related
I feel like I'm going round the houses on this one.
In summary, I have a Location model which has opening hours, modelled as opens_at and closes_at in the DB.
All times are stored as UTC in the database.
If I create a location in New York with opens_at set at 08:30 in my form and it gets saved to the DB as 08:30 UTC, why would I need to worry about timezones? I don't want to display the time in local time because the user would then see opening hours of 03:30.
Am I overthinking this? Do I only need to worry about timezones if I have users in multiple countries attending the same event at the same time?
As this is about physical locations, it feels to me that it wouldn't be needed.
If I create a location in New York with opens_at set at 08:30 in my form and it gets saved to the DB as 08:30 UTC, why would I need to worry about timezones?
Because 08:30 in New York is not 08:30 UTC. It's not even the same time for all dates.
It's 13:30 UTC when New York is observing Eastern Standard Time (EST, UTC-5)
It's 12:30 UTC when New York is observing Eastern Daylight Time (EDT, UTC-4)
So, if the location opens at the same time every day, then you must store it in local time. Otherwise you'll be off by an hour one way or the other following the next DST transition.
This can be an issue even for time zones that don't use DST, and even for non-recurring events, because the various governments of the world control the time zones within their borders. They can change whether to start observing DST or stop observing it, the dates and times that DST transitions occur, or their standard offset from UTC. Some give adequate notice when they make such changes, and others do not. There's always some non-zero chance that a given time zone might change its behavior between when you initially recorded the event and when the event takes place. If you recorded using local time, all you need to do is update the time zone data on your systems (which often happens automatically). However, if you recorded the event using UTC then you could be off when converting back after such a change.
In general, future events should always be stored in terms that the event is described - which is almost always in local time of some particular time zone. Store the IANA time zone ID (e.g., "America/New_York") with the location or event so that you can convert when you need to, but converting to UTC prematurely can lead to losing sight of the original information.
Save the "Always UTC" mindset for past or present events, such as timestamping a transaction.
Yes, I actually have run into this. If the user is only going to see the time in the local time zone, then it is not really necessary to save in UTC with time zone. You can save it in local time without time zone.
Reference: Postgres Time without Time Zone
Some developers will say that you should save it in UTC with the time zone, but I can see two arguments against it:
If you don't need it now and you may never need it.
You may not have access to the Time Zone now or may need extra code/complexity to implement and validate.
You can probably add it later if you know the time zone or lat/lon or address.
I have table which have a datetime field named date. When doing a POST in order to insert a new row, the date sent from the client (browser) looks like 2015-11-20T14:30:00+10:00 which is actually a correct date and timezone.
However, inside Postgres this date has been inserted as 2015-11-20 04:30:00.000000, which as you can see, is not at all the same as above. I know the problem is related to the timezone. But I cannot seems to figure out a fix.
For information, I have configured my app timezone :
class Application < Rails::Application
config.time_zone = 'Brisbane'
end
Ideas?
2015-11-20T14:30:00+10:00 means that the local time of 14:30 is 10 hours ahead of UTC. Your database field reflects the correct UTC value of 04:30. This is often the desired behavior, especially if the value represent a timestamp - the date and time something occured (past tense).
In PostgreSQL, there are two different types of timestamp fields (reference)
The TIMESTAMP WITH TIME ZONE field accepts an input that contains a time zone offset. It then converts the value to UTC for storage. On retrieval, it uses the session's timezone setting.
The TIMESTAMP, or TIMESTAMP WITHOUT TIME ZONE simply stores the date and time given, ignoring any offset, and not converting to UTC.
Most of the time, you should indeed use TIMESTAMP WITH TIME ZONE. You should only use TIMESTAMP WITHOUT TIME ZONE if you need to retain the local date and time value, such as in scheduling of future events and calculation of business hours. And for those scenarios, it often makes more sense to split date and time into separate DATE and TIME fields.
One last thing - if you can avoid it, avoid using Rails time zones and use standard tzdb zones. "Australia/Brisbane" is the full tzdb identifier equivalent to the Rails "Brisbane" time zone. Refer to the section on Rails time zones at the bottom of the timezone tag wiki.
I found this gem to be incredibly useful and easy for correctly setting the time https://github.com/kbaum/browser-timezone-rails
When i save a DateTime schedule_time to the DB, it saves according to my local time, but the timestamps (created_at) are saved apparently in UTC (7 hours ahead of my pacific time)
So if i submit the form setting my schedule_time for right now it will be 7 hours different than my created_at.
i need to show many users their times in their own selected zone, and i also need to compare times against each other, so i want all db entries to be in the same zone. Testing on my machine, my user has his zone saved as Pacific (-7:00), but its saving schedule_time in local time, not really UTC, so when i try to display the time back like this:
#item.schedule_time.in_time_zone(#user.time_zone)
it actually takes the stored datetime and subtracts seven hours from it giving me 7 hours before i wanted. i think the best thing is to just store all the datetimes in a uniform way so i can compare them easily.
changing this value config.time_zone = 'UTC' does nothing to change the stored format of my datetime. it stores in my local time regardless, while storing the timepstamps in real UTC.
ive also tried to reformat the datetime before storing it, with in_time_zone(#user.time_zone) but it had no effect on the stored time.
if i can just get schedule_time stored in UTC just like my timestamps are stored i could make this work! any ideas?
If you want to store schedule_time converted to UTC before storing it in the database, you can include a before_save callback in your Item model to convert it as follows:
before_save { |item| item.schedule_time = item.schedule_time.utc }
sorry i was totally on the wrong track.
the issue was with the jquery date picker i was using (will_pickdate). it returns a date and time but with a +0000 time zone offset. by default, the picker autofills with the current local time, but when i submitted that, rails basically thought it was receiving a time in UTC and added it as my local time but with +0000.
in order to store the date properly i have to keep the time and date from the picker intact, but just shift the +0000 part to something appropriate:
my_time.change(offset: user_time_zone_offset)
Right, this is a bit confusing for me, so I'm going to try and explain from the top!
I have a rails web app. It's an internal company app and will only be used in the UK.
One of the things the app does is manage meetings.
Meetings have a date & time when they start. There's a date/time picker on the form which allows the user to pick the date & time the meeting is for. I save this date AS IS into the database. All meetings last 2 hours, so the end time is simply start + 2 hours.
Example:
2013-06-23 6:45PM in the form is stored in the db as 2013-06-23 18:45:00
2013-12-23 6.45pm in the form is stored in the db as 2013-12-23 18:45:00
Note that the first date is during Daylight Savings (BST) and the second is during GMT. I don't actually care whether it is GMT or BST: the meeting happens at that time, absolutely.
Inside the rails webapp, I simply print out the exact date & time from the DB - formatted nicely, of course!
Now, at some point I send an email to the organiser of the meeting, and the person they're meeting with. This email tells them the the date & time of the meeting etc, and also includes an iCal (.ics) file for them to put into their (Outlook usually, but also Apple or gmail) calendar.
The issue I am having is that (using the above examples) Outlook shows the meetings like this:
Meeting #1: Start: 23/06/2013 7:45pm, End: 23/06/2013 9:45pm
Meeting #2: Start: 23/12/2013 6:45pm, End: 23/12/2013 8:45pm
Note that it has adjusted the first one because of the BST/GMT thing.
The text of the .ics file contains this code:
Meeting #1:
BEGIN:VCALENDAR
...
DTEND:20130623T204500Z
DTSTART:20130623T184500Z
...
END:VCALENDAR
Meeting #2:
BEGIN:VCALENDAR
...
DTEND:20131223T204500Z
DTSTART:20131223T184500Z
...
END:VCALENDAR
So I am encoding the dates/times using the Z timezone (UTC). I understand this is why Outlook mis converting the UTC time into the BST time for #1 and leaving #2 alone (because GMT == UTC)
My question is: how do I stop this happening? I want the time the meeting is scheduled for to be the absolute, actual time, regardless of GMT/BST: 6:45pm
Should I be storing the date-times as UTC in the DB? How would this be done (I assume it would apply to all dates, not just meeting start dates). And how to re-convert them back into the actual datetime when I display them in the webapp?
Extra:
I have an entry in my initializers/time_formats.rb like this:
:ical => "%Y%m%dT%H%M00Z"
So dates come out like "20130623T184500Z". I use this when building the ics. And this I think is the issue - if the date/time is during BST I don't want to be using Z, but something else?
Your problem is your date/time format. You have:
DTSTART:20130623T184500Z
in your .ics file and this corresponds to 19:45 BST (as British summer time is UTC+1).
There are a few things you should do. First, you can simply remove the 'Z' from the end of your dates. This means that the times inherit the timezone of the calendar, or the underlying application.
This will work assuming that the machines which are running Outlook are all in the Europe/London timezone. If not, or if you want to be a bit safer, you should also specify the following after your BEGIN: VCALENDAR line:
X-WR-TIMEZONE:Europe/London
This specifies the default timezone for all dates which are not specified explicitly.
Finally, if this does not work for any reason then you need to define your datetimes explicitly. First you need to add a timezone definition for Europe/London to the calendar. The info you need is available at http://www.tzurl.org/zoneinfo-outlook/Europe/London.ics. Then you need to ensure that all datetimes are of the format:
DTSTART;TZID=Europe/London:20130623T184500
This last approach is the best, as it means that if your requirements expand to other timezones you will be able to handle them relatively easily.
Sorry to answer this myself, but in case anyone else runs into this here's what I found was the cause of my particular issue. Note that the answer above re timezones also makes sense!
My rails app is storing UTC datetimes in the DB (as is default)
But, it also thought it's own timezone was UTC, which also seems to be the default.
The upshot of that is essentially it was storing local dates, local to UTC anyway. Changing the app to know it was sitting in Europe/London made it so the dates in the DB are all now accurately UTC (meaning, they're an hour off if I'm currently in BST)
I can now use the Z datetime format in iCals, and outlook and the rails app both convert the UTC date back into the actual datetime for the viewing-user's locale (Europe/London for everyone at the moment). This is what I wanted.
I'm using Rails 3.2.8. When I generate a scaffold with a time field or datetime field. The HTML form field gets pre-populated with the current date/time in UTC. Great that it's pre-populated with the current date/time, but because it's in UTC, we have to change the time back 7 hours every time (which will sometimes require setting the day back 1 also, possibly month and year too). And then it seems the UTC time gets stored in the database, so I'll have issues displaying/editing it as well if I recorded it in our local time.
I looked at the Ruby documentation for the form helpers to deal with local time better, but I don't see anything relevant.
What's the best way to deal with editing and displaying dates and times in Rails?
UPDATE: To clarify, I like the idea that UTC time is stored in the database. I just want the time_select and datetime_select form helpers to edit the times in the user's local timezone. And, of course, I want to easily display the time in the user's local timezone.
You have to set the time zone to display on a per-user basis somewhere in a before/around_filter. This has to be done like:
Time.zone = "Kyiv"
An example can be found in its API: http://api.rubyonrails.org/classes/Time.html#method-c-zone-3D.
Run the rake time:zones:all to see all of them.
All the conversions has to be handled for you behind the scene.
This has helped me in the past. You can do things like:
Time.now.in_time_zone("Central Time (US & Canada)")
See Rails: convert UTC DateTime to another time zone