I am programming in Delphi and consuming an API that returns an XSDateTime representing an appointment timeslot. When I try to create a local datatime the time is being converted to my EST timezone (Z-05:00 or Z-04:00 depending on DST). I need the time to remain in the original timezone of CST (Z-06:00). I am currently formatting the time as follows:
aApptListing := FormatDateTime('yyyy/mm/dd t', aSlots[i].StartDateTime.AsDateTime);
where StartDateTime comes in as the time in CST (Z-06:00). How can I keep the original time for CST? For instance, if the date/time comes thru the API as '2011-12-25T08:00:00-06:00' I want to show 12/25/2011 # 8:00 AM, not 9:00 AM which would be EST.
It looks like the following should work:
with aSlots[i].StartDateTime do
aApptListing := FormatDateTime('yyyy/mm/dd t', EncodeDateTime(Year, Month, Day, Hour, Minute, Second, 0));
Related
I am using Esper & I need to filter events by their timestamp. The events come from an external source.
The challenge is that the cutoff instant is at a different timezone than the events` timestamp, e.g. the cutoff instant is at 3:30 CET (e.g. Prague time) while the timestamp field of the event is at UTC.
This poses a problem when the timezone shifts to Daylight Savings Time, because the cutoff instant needs to be modified in the query. E.g. in this case, if the cutoff instant is 3:30 CET, during winter time it would be on 2:30 UTC and during DST it would be on 1:30 UTC. It means that I have to change the query when the time shifts into and out of DST.
This is the current query:
SELECT *
FROM my_table
WHERE timestamp_field.after( timestamp.withtime(2,30,0,0) )
I would like to have a robust solution that will save me the hassle of changing the cutoff timestamp queries every few months. Can I add the timezone to the query statement itself? Is there any other solution?
It may help to add an event property to the event that represents UTC time i.e. normalize the event timestamp to UTC and use the normalized property instead.
The query could also use a variable instead of the hardcoded numbers. Another option would perhaps be changing Esper source to take in a timezone for some func.s
After struggling unsuccessfully with trying ot do it in the WHERE caluse or using a Pattern, I managed to solve the issue using a [Single-Row Function plugin][1].
I pass the plugin function the cutoff hour, timezone & event timezone and compute the cutoff hour in the event's timezone.
My query changed to:
SELECT *
FROM my_table
WHERE timestamp_field.after( timestamp.withtime(
eventTZHour(2, 'UTC', 'Europe/Prague'), 30, 0, 0) )
I added the Java implementation in a class:
public class EsperPlugins {
public int eventTZHour(int hour, String eventTZ, String cutoffTZ) {
// return tz calculations
}
}
and finally registered the plugin in esper.cfg.xml:
<esper-configuration>
<plugin-singlerow-function name="eventTZHour"
function-class="EsperPlugins"
function-method="eventTZHour"/>
</esper-configuration>
[1]: http://www.espertech.com/esper/release-5.2.0/esper-reference/html/extension.html#custom-singlerow-function from esper's docs
I'm working on a Rails application which stores all dates to PostgreSQL as "TIMESTAMP WITHOUT TIME ZONE". (Rails handles the time zone on the application layer which for this application is "Europe/Berlin".) Unfortunately, Daylight Savings Time (DST) becomes an issue.
The simplified "projects" table has the following columns:
started_at TIMESTAMP WITHOUT TIME ZONE
duration INTEGER
Projects start at started_at and run for duration days.
Now, say there's only one project which starts on 2015-01-01 at 10:00. Since this is "Europe/Berlin" and it's January (no DST), the record looks like this on the database:
SET TimeZone = 'UTC';
SELECT started_at from projects;
# => 2015-01-01 09:00:00
It should end on 2015-06-30 at 10:00 (Europe/Berlin). But it's summer now, so DST applies and 10:00 in "Europe/Berlin" is now 08:00 in UTC.
Due to this, finding all projects for which the duration has elapsed by use of the following query does not work for projects which start/end across DST boundaries:
SELECT * FROM projects WHERE started_at + INTERVAL '1 day' * duration < NOW()
I guess it would be best if the above WHERE did the calculation in timezone "Europe/Berlin" rather than "UTC". I've tried a few things with ::TIMESTAMTZ and AT TIME ZONE none of which has worked.
As a side note: According to the PostgreSQL docs, + INTERVAL should deal with '1 day' intervals differently from '24 hours' intervals when it comes to DST. Adding days ignores DST, so 10:00 always stays 10:00. When adding hours on the other hand, 10:00 may become 09:00 or 11:00 if you cross the DST boundary one way or another.
Thanks a lot for any hints!
I think you've got two strategies for avoiding headache:
Let Rails handle everything to do with Timezones, so Postgres doesn't have to at all
or
Let Postgres handle everything to do with Timezones, so Rails doesn't have to at all
Mixing the two will always be a pain, and is basically what's causing your problems now. I'd go with strategy 1 (let Rails handle it). To do this, your Postgres database should store a start time, and a finish time, both in UTC. duration may be a thing in your user interface still, but if a user enters a start time and a duration, then you should calculate a finish time, and store that finish time in your database. The start time the users enters, and the finish time that you calculate in your app, with both be timezone-specific, and you just let Rails handle the conversion to UTC when it saves to the database.
Your query would then be simply:
SELECT * FROM projects WHERE finished_at < NOW()
(BTW, You could also store the duration in your database, but it's superfluous, since it can be calculated from the start time and finish time)
I've created a function which calculates ended_at by adding duration days to started_at honoring DST changes of a given time zone. Both started_at and ended_at, however, are in UTC and therefore play nice with Rails.
It turns started_at (timestamp without time zone, implicit UTC by Rails) to a timestamp with time zone UTC, then to the given time zone, adds the duration and returns the timestamp without time zone (implicit UTC).
# ended_at(started_at, duration, time_zone)
CREATE FUNCTION ended_at(timestamp, integer, text = 'Europe/Zurich') RETURNS timestamp AS $$
SELECT (($1::timestamp AT TIME ZONE 'UTC' AT TIME ZONE $3 + INTERVAL '1 day' * $2) AT TIME ZONE $3)::timestamp
$$ LANGUAGE SQL IMMUTABLE SET search_path = public, pg_temp;
With this function, I can omit having to add ended_at as an explicit column which would have to be kept in sync. And it's easy to use:
SELECT ended_at(started_at, duration) FROM projects
Background: I'm building an app with Angular JS as web interface and Rails API. The problem I am having is passing a date from Angular to Rails.
Issue: I have a form with a Date of Birth date field, when a user inputs his DOB say March 1st, 1985, Angular interprets it as 1985-03-01 00:00 +0800 (if you're in Hong Kong or Singapore) and sends a request to Rails. The first thing Rails does with it is to convert it to UTC, which means the datetime is now 1985-02-28 16:00 UTC. Therefore, when the date is saved to the database date column, it becomes Feb 28, 1985.
Solution for now: What I'm doing now is on Angular side, I get the Timezone offset hours and add it to the date, so instead of 1985-03-01 00:00 +0800, it is now 1985-03-01 08:00 +0800. When Rails get it, it converts to 1985-03-01 00:00 UTC and so saves the correct date to db. However, I believe this is a better alternative to tackle this issue.
Thinking about parsing just the date in Rails, yet the params[:dob] I see is already UTC by the time I get it. Would love to know if there is a better practice than my current solution. Thank you for any comment and feedback.
This problem is actually quite common, and stems from two separate but related issues:
The JavaScript Date object is misnamed. It's really a date + time object.
The JavaScript Date object always takes on the characteristics of the time zone for the environment in which it is running in.
For a date-only value like date-of-birth, the best solution to this problem is to not send a full timestamp to your server. Send just the date portion instead.
First, add 12 hours to the time, to use noon instead of midnight. This is to avoid issues with daylight saving time in time zones like Brazil, where the transition occurs right at midnight. (Otherwise, you may run into edge cases where the DOB comes out a day early.)
Then output the date portion of the value, as a string in ISO format (YYYY-MM-DD).
Example:
var dt = // whatever Date object you get from the control
dt.setHours(dt.getHours() + 12); // adjust to noon
var pad = function(n) { return (n < 10 ? '0' : '') + n; }
var dob = dt.getFullYear() + '-' + pad(dt.getMonth()+1) + '-' + pad(dt.getDate());
Another common way to do this is:
var dt = // whatever Date object you get from the control
dt.setHours(dt.getHours() + 12); // adjust to noon
dt.setMinutes(dt.getMinutes() - dt.getTimezoneOffset()); // adjust for the time zone
var dob = dt.toISOString().substring(0,10); // just get the date portion
On the Rails side of things, use a Date object instead of a DateTime. Unlike JavaScript, the Rails Date object is a date-only object - which is perfect for a date-of-birth.
I have a time field in table "timestamp without time zone". When record is saved to database, the utc time might be a different day compared to the local time. However, I need to group the records by date. Hence, I am doing something like this:
result = transmissions.joins(:report).where('reports.time::timestamp::date = ?', record.time.to_date)
The problem is if the utc date is on a different date than local time, then that record is not included in result. Any ideas how to get the right result?
And apparently I cannot change the "without time zone" either:
Rails database-specific data type
It says:
"concluded that the default ActiveRecord datetime and timestamp column types in schema migrations cannot be modified to force PostgreSQL to use timestamp with time zone."
So I have no idea how to group by date, as obviously something like this is wrong:
Unit.where(id: 1100).first.reports.order("DATE(time)").group("DATE(time)").count
=> {"2013-12-14"=>19, "2013-12-15"=>5}
That return value is completely wrong. All 25 records should be on 2013-12-14 and 0 records on 2013-12-15.
Assuming your records are timestamped with a particular UTC offset, you can try passing in the start and end times of the date in question in UTC format to your query:
result = transmissions.joins(:report).where('reports.time >= ? AND reports.time < ?', record.time.midnight.utc, (record.time.midnight + 1.day).utc)
Explanation:
midnight is a Rails method on an instance of Time that returns the Time object that represents midnight on the date of the original Time object. Similarly, record.time.midnight + 1.day returns the Time object representing midnight of the following day. Then, converting both Time objects – which are presumably timestamped in a standard UTC offset – to UTC creates a time period representing midnight-to-midnight for the system timezone in UTC format (not midnight in UTC time), which is precisely what you're seeking to query.
How about something like result = transmissions.joins(:report).where('reports.time >= ? AND reports.time <= ?', record.time.beginning_of_day.utc, record.time.end_of_day.utc)
The .utc part may not be necessary.
I create multiple scheduled objects with different scheduled_on attributes. For example, each object would have a date to land on 4:00pm the first of every month.
Once one of those objects hits a timezone change. The app intelligently configures it an hour ahead or behind so that its relative to its parent's timezone.
The problem is that the app will save an object as 4:00PM (in Pacific Standard) for times that will eventually be displayed as (PDT or an hour ahead or 5:00pm). This would mean that I need it to save an hour off in UTC so that when the time comes about, it will display as 4PM regardless of what timezone we are in.
Whats the best technique for ensuring this in Rails?
I'm going to answer this question by pointing out some good things to know about adding time in Rails in relation to timezone.
When you add time, time is allocated in UTC to stay the same time despite timezone changes :
t = Time.now
-> 2012-08-10 13:17:01 +0200
t + 90.days
-> 2012-11-08 13:17:01 +0100
A DateTime will not do this. A DateTime will go up an hour or down an hour in the same TimeZone it began in :
dt = DateTime.now
=> Fri, 10 Aug 2012 13:16:54 +0200
dt + 90.days
=> Thu, 08 Nov 2012 13:16:54 +0200
But a DateTime is the only way to get the number of days between two dates which you can do by subtracting two DateTimes. This, you can't do with a Time, because when substracting a time, it will not divide by a perfect 24 hours, you'll get an irrational number because of the timezone switch.
This is specific to my issue. But I solved my problem by converting my Time to DateTimes to find the number of days in distance, and then reconverted back to time to find a later time in UTC relative to a TimeZone change :
original_job.to_time + ( new_date.to_datetime - original_job.to_datetime ).to_i.days