A lot of questions have been asked about this subject. The best answer that I found is this one: How to set local timezone in laravel
So the main rule is to keep all database entries in the same timezone.
But I have a specific case where this answer does not work for me. For some models, I have only a date (no datestamp). Example: suppose that I only store the date of when this question was asked (= 2018-01-25). However in Europe it is already 2018-01-26. Someone has a solution for this?
Changing my date field to a datestamp? What with existing dates?
You can use this library jamesmills/laravel-timezone
OR
If you need custom configuration:
Configure your app timezone to UTC.
'timezone' => 'UTC',
You can store different timezones in database column.
When outputting/displaying dates, just format it to use that timezone.
$timezone = 'America/Vancouver';
$model->created_at->setTimezone($timezone);
created_at and updated_at are automatically converted to carbon instances, which makes this easier. If you have other dates that you're using, add them to the protected $dates array on the model and laravel will convert them to carbon instance too. Then you can use carbons setTimezone() to change the date/time to the timezone.
If you're only talking about a date, then there is no time component and thus time zones are irrelevant. For this reason, most platforms do not have a separate date-with-zone type.
You're correct that not every time zone experiences the same date at all times, and that the start of a date and the end of the date occur at different times in different time zones. However, did you notice that in the prior sentence that I had to use the word "time" to rationalize about these points? :-)
Because date and time zone don't come together without time, there's no purpose in keeping them in the same field. Instead, keep two fields in your model - one for the date, and one for the time zone. In many cases, you may even find they belong in two different models.
As a use case example, consider birthdays. Mine is 1976-08-27. That's all it is - just a date. The time zone of my birth is irrelevant, and so is the time zone I'm located in - until I want to evaluate whether it's currently my birthday (or how long until my birthday, etc.) For those operations, my current time zone is important, and so is the start time-of-day and end time-of-day of that time zone. Thus - two different fields.
Related
I created a QueryExpression with one of the Conditions set to ("dev_lastremarketingtime", ConditionOperator.OlderThanXHours, 1);
The intent is the retrieve multiple records that are an hour after the value of dev_lastremarketingtime.
There are records in the table that meet this criterion, however, they are not returned. When I examine the record (RetrieveMultiple of a specific record this time) it seems that the times used for comparison are not consistent.
For example, when viewing the account record in question, the dev_lastremarketingtime's value as shown on the account form is 5/17/2017 8:57 PM. the internal is time 5/18/2017 12:57:27 AM. The wall clock at the time of the test shows 5/17/2017 10:38:11 PM (or 5/18/2017 2:38:11 AM UTC). This record should have been returned by the query (the current time is more than one hour after the value of dev_lastremarketingtime)
If I wait a few hours and run my app again, the expected records are retrieved.
It seems, therefore, that the Query expression with the ConditionOperator.OlderThanXHours is comparing the current Eastern Daylight time with the record's UTC time.
How can I get this query to compare the same time zones (I don't think it matters which one)?
(My Personal options include the setting for Eastern Time
Instead of using the OlderThanXHours operator, maybe try using "less than", which provides control of the DateTime value to filter on.
This way you can use the UTC time minus an hour, like this:
var qe = new QueryExpression("myentity");
qe.Criteria.AddCondition("dev_lastremarketingtime", ConditionOperator.LessThan, DateTime.UtcNow.AddHours(-1));
I am working on my first application for mac which uses Core Data. Since I don't have much software development experience I would like to ask the more experienced developers the following question:
When entering data in some of the forms, user will have to enter a date in couple of the forms. Since app will be on app store and people from different continents will download it (I hope so) I am thinking of allowing the user to select his preferred date format from the preferences panel that I have in my app.
But I am wondering what will happen if after entering 500 or more records, he decide to change the date format again? Will that cause a mess in core data eventually?
Is this good idea or I should keep things simple and just get the system date (user computer date format) and use that date format? What would you do? Any advice will be deeply appreciated.
My advice is to keep date as timeinterval. You can see such method for NSDate.
The interval between the date object and 00:00:00 UTC on 1 January 1970.
So if you get NSDate object from NSDatFormatter object you will be able to obtain time in seconds since 1970. You could store this value in Core Data and use it later for creating NSDate objects. You will be able to use it for different locales and time zones as well as use the correct format.
'Dates' is complex topic and I suggest you to read guides about dates and date formatters.
First is to decide how you should store the date. The answer here is as an NSDate. The NSDate is a single unique precise point in time, thus it in a sense stores both date and time.
This means that for example 1 PM in Berlin and 8 pm in Kuala Lumpur will be the exact same NSDate value (during winter months) but 2 pm in London and 2 pm in Paris the same calendar date will not be the same NSDate value. This is a quite complex topic, read the date and time programming topics documentation from Apple.
Then as you say you need to allow you user to input the date. The way to do that is to use a NSDateFormatter tied to your input control. The formatter can be defined to be as per system settings, which means you will get the localisation you are seeking for free, so that is in fact easy.
The tricky thing you are really facing is to determine what you are really looking to store if it is only the calendar date without an associated time you want to store. For example you decide store the date combined with 12.00 noon in the local timezone. Then if the user shifts to another timezone more than 12 hours away the date may be displayed as the previous date or the next. The safest bet is to store the date combined with 12:00 noon GMT as this is in the middle of the time zone range. There are a few locations 13 and 14 hours off that could exhibit the mentioned problem anyway, but these are small atolls in the pacific and could possibly be safely ignored.
However the the best thing is if you can in fact determine that what you are looking to store is really a precise point in time rather than a date (which is a 24 hour fuzzy definition). For example in a calendar app an event usually takes place at a specific time on a specific date, then store that time and date.
I am currently storing events of some entities in UTC time but I am not sure if I should do that in this case. Imagine there's an event at 10pm local time (-4h UTC) and a mobile App fetches "todays events". This could e.g. look like this:
App sends request to fetch all clubs in the near location
After receiving all clubs it sends a request to get all events for today. It therefore sends the local time Sun. 10pm to the server.
The server would convert the local time of the mobile device to UTC Mon. 1am and fetch all events from Monday. But of course that was not what I wanted.
Fetching all events from the clubs and convert them to their local time using their local time offset information is not really a great solution.
So wouldn't it be better to just store all events in local time? In that case the mobile App would send its local time to the server which would be able to query all events from the clubs in local time as well.
This sounds much simpler to me but I am not sure if I overlook something.
So what would I do in this case?
Yes, storing everything in UTC is probably the best solution.
You don't say how you are "storing" the dates/times, but if you are using Dates or Joda equivalents, then you should know that their underlying representation is effectively in UTC (they represent a moment in time as an offset in milliseconds since the "Epoch", which is Midnight, Jan 1, 1970 UTC). These dates only have a timezone when you format them as Strings.
Most databases do something similar (store the date in a common timezone, usually UTC). The major exception that I've found is the generally available date-time related column types in MS SqlServer which by default store everything in the local timezone of the server.
Also be aware that if you use SQLite, and you store a date/time by passing a String in SQL that contains a timezone, SQLite will store it without warning, but will ignore the timezone and assume that the timezone is UTC, giving you a result other than what you might expect.
For more on this, see my (old) blog post at http://greybeardedgeek.net/2012/11/24/java-dates/
The other answer is correct. Some more thoughts here.
A time zone is more than the offset from UTC mentioned in the Question. A time zone is also the set of past, present, and future rules for anomalies such as Daylight Saving Time. You should refer to a time zone by its proper name, continent plus Slash plus city or region. Never use the 3-4 letter codes such as EST or IST.
To search for events in the user's "today", you must know the user’s time zone. For example, a new day dawns earlier in Paris than in Montréal. After the stroke of midnight in Paris we still have a few hours of “yesterday” left to go in Montréal.
While you can make a guess as to the user’s time zone, the most reliable way is to ask the user.
DateTimeZone zone = DateTimeZone.forID( "America/Montreal" );
DateTimeZone now = DateTimeZone.now( zone );
DateTime today = now.withTimeAtStartOfDay();
DateTime tomorrow = today.plusDays( 1 );
// Search for events that start >= today AND that start < tomorrow.
To search Joda-Time objects, use the Comparator built into DateTime. That comparator works across objects of various time zones.
To query a database, convert that pair of DateTime objects into java.sql.Timestamp objects. You do that by extracting and passing the count of milliseconds since the epoch of 1970 in UTC.
long m = today.getMillis();
java.sql.Timestamp tsToday = new java.sql.Timestamp( m );
I assume that application code should store time in database always as UTC ( punch me if I am wrong)
Now lets say I want to query everything between 23-mar-2013 to 24-mar-2013 . Should I create a time object and then query something like "23-mar-2013:00:00:00UTC" to "24-mar-2013:24:00:00UTC" or querying just by date is right "23-mar-2013" to "24-mar-2013".
Now the problem comes when I am not in UTC and in a time zone like -7:30 .
Now date queries would go wrong..
So does that mean I should query always with time ?
I am talking in concern to ElasticSearch, Tire, Ruby ( But I think that shouldn't matter)
The implementation absolutely does matter. Querying against one database or another is very different depending on how that database stores date / time values. I suggest you edit your question and make it specific for the technologies that you are using. Show some code if you can.
In general though, you are mixing two concepts and you should probably try to separate them mentally.
The moment something happened, an event time, can be measured by a DateTime combined value - represented as either UTC, or as a value that is offset from UTC where the offset is known. This is often referred to as "Instantaneous Time", "Universal Time", or "Physical Time".
The values that we give to dates and times when talking about them locally, such as "Today", "Yesterday", or "March 29, 2013". Even when we have a time, we are talking about a fraction of a day on a calendar. This is often referred to as "Calendar Time", "Local Time" or "Civil Time".
You can always query and do math with Instantaneous Time. It's unambiguous. However, the concept of "Today" is meaningless. There is no observer to mark the end of one day and the start of the next. (One could argue that the observer is in London, but that's not true during BST.)
Calendar Time is only suitable for querying or math when you have day-level precision and only one observer. So it usually makes a poor representation of something meant to be universal, like an event.
Let's go back to your original question. You said:
I want to query everything between 23-mar-2013 to 24-mar-2013
Right there - you have a problem. What is the context? Who's calendar dates are you talking about? Even though you said March 23, you probably don't mean March 23rd at midnight UTC to March 24th at midnight UTC. You probably mean some other calendar's midnights.
Keep in mind that not every day is 24 hours in length. When time zones switch on and off of daylight savings time (or summer time), the days could be 23 hours or 25 hours in length.
So what to do? First, you need a Time Zone database (like the IANA/Olson/TZ/TZDB/ZoneInfo database for example) Here is one implemented in Ruby.
Now, you need to to know the local time zone of the user. That is - the person that is asking the question that you are showing the query results to. That will involve your own application logic, maybe a selector or picker. If this is a web app, you might want to look at this map-based timezone picker, or at jsTimeZoneDetect.
You should always store events with instantaneous time. Let's just say you store events as UTC (although you might use an offset, we'll ignore that for now).
So you need to know for the date range that the user wants, what UTC times do the start and end dates of your query map to? For example, say we are in India using the Asia/Calcutta time zone. We would convert 23-mar-2013 00:00 - 24-mar-2013 00:00, to the UTC equivalent 22-mar-2013 18:30 - 23-mar-2013 18:30.
Then you can use those UTC DateTime values to query the database.
When you return the results to your user, you will probably want to convert UTC back to local time so they understand the results they are looking at.
You should also read the many great suggestions in this post.
We have a reporting application where all DateTimes are stored in UTC in the database (SQL server 2005)
The reporting application works simply be retrieving a DataTable and binding to a DataGrid displaying the information.
If we know the logged in users time zone (e.g. +3 GMT), is there any way to update the DataTables dates which are in UTC to now display in the users time zone?
We know we can spool thorugh each column/row in the DataTable and do a conversion but is there a better more efficient way?
I would modify the time as it is displayed to the user. Keep how it is stored consistent, but also store what their timezone is, and then modify the UI to show the correct local time. For example, if their time zone is Central Standard Time, then you could use something similar to the following code:
SomeDataObject someDataObject = new SomeDataObject();
someDataObject.TimeZone = -5; //UTC Timezone for Central Standard Time
someDataObject.Time = DateTime.Now;
DateTime someTime = someDataObject.Time;
someTime.Add(someDataObject.TimeZone); // Display this back to the user
If using .NET, there's a built in class that was made precisely for this purpose. TimeZoneInfo (http://msdn.microsoft.com/en-us/library/system.timezoneinfo.aspx) as taken from the article:
A TimeZoneInfo object can represent any time zone, and methods of the TimeZoneInfo class can be used to convert the time in one time zone to the corresponding time in any other time zone. The members of the TimeZoneInfo class support the following operations:
Retrieving a time zone that is already defined by the operating system.
Enumerating the time zones that are available on a system.
Converting times between different time zones.
Creating a new time zone that is not already defined by the operating system.
Serializing a time zone for later retrieval.
Hope this helps.