The back-end is C# and SQL Server.
I save logging activity date times from different time zones in UTC in my DB. I need to populate a globally distributed front end so it localizes the logged UTC time based on where the front end is located, which will be known e.g. PT, ET. It also needs to handle daylight savings time which is where I'm running into difficulty.
As the UTC offset changes based on the time of the year because of daylight savings time, is there a way for me to find out what the UTC offset is in C# given that I know the date/time and the time zone.
is there a way for me to find out what the UTC offset is in C# given that I know the date/time and the time zone
Technically you shouldn't need to find out this information, the underlying system clock/calendar/what-have-you should take care of it. (I'm sure anybody who has worked on date-time logic will attest to the fact that it is non-trivial to say the least.)
Ideally, any time you need to convert a time zone, you have three things:
A DateTime object representing the value to be converted.
A TimeZoneInfo object representing the known current format of the DateTime object (in this case UTC).
A TimeZoneInfo object representing the target time zone.
Given those things, any time you want to display the DateTime to a localized user, you'd use something like TimeZoneInfo.ConvertTime to perform the conversion. This should ideally be done as close to the UI as possible so that backing logic is always consistently performed in UTC.
Related
Currently I have an UTC date which I have to convert to different time zone based on where my client time zone is.
This is the code am currently using:
var timezoneInfo = TimeZoneInfo.FindSystemTimeZoneById(timezone);
var clientTime = TimeZoneInfo.ConvertTimeFromUtc(createDateTime, timezoneInfo);
I know this automatically uses the daylight saving time and provide me the current time based on time zone.
I have a boolean which determines whether is daylight saving time is enabled or not. The above method doesn't work well based on my boolean value.
Is there a inbuilt method or code that converts UTC to different time zone without daylight saving time?
It is generally a bad idea to provide a boolean daylight saving time flag in your application at all. Time zones are all about the actual local time in a particular area, and that always includes whether the government that controls that time zone has decided if daylight saving time applies or not. In other words - it's not up to the user, it's up to their government. Microsoft and the IANA time zone community go out of their way to ensure the time zones accurately reflect those governmental decisions.
If you really must do this, you could consider either using the TimeZoneInfo.BaseUtcOffset property, or you could inspect the result of TimeZoneInfo.IsDaylightSavingTime to decide whether to subtract time from the result. However, both approaches suffer from edge cases that will give you errors in cases where the standard time offset has changed unrelated to daylight saving time. Additionally, not all time zones shift by a full hour for DST, there's one that shifts by 30 minutes.
Ultimately, my recommendation would be to keep your code as-is and not try to use that boolean flag. Instead, go back to the UX or wherever that flag originates and remove it.
We have an application related to aviation, and specifically flights.
Times have to be stored in local, so I chose to use UTC Time + an offset, but then now I realize it is a bad choice:
By storing the timezone as an offset, I lose track of the original timezone and this has implications when dealing with daylight savings.
For example I can store a time in Alpine, UT as UTC time and a -6 offset and also a time in Phoenix, AZ as UTC time and a -6 offset.
But when daylight saving comes, the time will change in Alpine, but not in Phoenix.
So, I need to store the proper timezone and I have seen that there are also different lists with a different syntax, so I am assuming there are different standards.
In C#, what would be the best option to store a local time with the local time zone to make it work with daylight saving changes?
From the discussion in the question's comments, I understand that you are working with flight time schedules - that is, the time a future flight is intended to depart. This is indeed a case where the local time is more important than the UTC time.
Since you have the local time and location of departure (ex: 5:00 PM in Salt Lake City), then you should be storing in your database of scheduled departure times two values:
17:00 - The relevant local time of the departure
SLC - The location where the time is relevant
If this is a specific occurrence of this flight, then you should store the date as well:
2018-06-01T17:00 - The specific relevant local time of the departure
SLC - The location where the local time is relevent
These are the details that are contextually relevant to your business use case. Do not lose sight of them by converting them to UTC.
That said, you might consider storing them as a DateTimeOffset (2018-06-01T17:00-06:00), which makes converting to UTC trivial for a given instance. However there are two problems with this approach:
It cannot work with recurrences, because the offset may change.
Even for a single instance, the offset might change - if the government controlling the time zone decides to change their standard offset or daylight saving time rules before that occurrence takes effect. If you do take a DateTimeOffset approach, or a UTC-based approach, you must be prepared to recalculate future events in the face of such changes. (For more on this, see my blog articles: On the Timing of Time Zone Changes and Time Zone Chaos Inevitable in Egypt. There are countless other examples.)
With regards to the location - because you are working with data that is contextually applicable to the airline industry, I recommend using IATA airport codes like the SLC that I showed above. In other contexts, one might store an IANA time zones identifier like America/Denver, or a Windows time zone identifier like Mountain Standard Time.
You may find my "Airport Time Zones" gist (code and output table) useful for working with IATA airport codes. You'll have to decide how that data will flow through your system. If you are running on Windows and want to use the TimeZoneInfo class to convert times to different time zones, then use the Windows time zone IDs shown there. If you want to use the IANA time zone IDs instead, consider using Noda Time, or you can use my TimeZoneConverter library. There are several different options here, so explore them all carefully and pick ones that make sense to you.
Noda Time would be a great choice, IMHO. Not only would you get excellent time zone support, but you'd also be able to use types like LocalTime or LocalDateTime which align well with the scenarios described.
As I wrote in my comment, do not store local dates. Instead, store datetime values as UTC, and convert to local datetime when you need to display it.
You can use the ConvertTimeFromUtc method of the TimeZoneInfo class for that.
This means you will have to also keep a list of locations and whatever TimeZoneInfo they are associated in - For example,
Jerusalem would be associated with Israel Standard Time,
Rome with W. Europe Standard Time,
Hawaii with Hawaiian Standard Time
and so on. (I'll bet you can find such a list online somewhere.)
Please note that the ConvertTimeFromUtc method handles the daylight savings problem for you as well.
Then you can do something like this to get the local time by location:
DateTime GetLocalDateByCityName(DateTime utc, string cityName)
{
var timeZoneInfoId = GetTimeZoneInfoIdByCityName(string cityName);
return TimeZoneInfo.ConvertTimeFromUtc(utc, TimeZoneInfo.FindSystemTimeZoneById(timeZoneInfoId);
}
And of course, in GetTimeZoneInfoIdByCityName you get the TimeZoneInfoId for the specific city.
You should use TimeZoneInfo.ConvertTime to convert DateTime between time zones if you need to handle Daylight Savings.
TimeZoneInfo.ConvertTime(myDateTime, timeZone);
TimeZoneInfo.ConvertTime(myDateTime, fromTimeZone, toTimeZone);
I'm working on an ASP.NET/C# application, which supports time zones.
First let me explain the flow of the application, I'm storing an object for purchase order. So it has the datetime field in it.
I'm storing that datetime as UTC in Database, and binding it in grid (according to the client's timezone).
In the Page_Init method of the first page, I had used a javascript code which will detect the client's timezone, and return appropriate offset.
In the Page_Load method, I'm getting that javascript return value (offset) and comparing it with the offset of each zone in TimeZoneInfo.GetSystemTimeZones().
When comparing the offset, I'm getting a TimeZoneInfo object (for example) "(UTC-08:00) Baja California", "(UTC +05:30) Chennai,Kolkata"
Using that particular TimeZoneInfo object, I'm converting the UTC datetime (which is stored in DB) to the client's timezone.
As by the above flow, the application works fine for some timezones.
The problem is, if when I change timezone of client machine to (UTC -8:00), the client machine shows the timezone name as "(UTC-08:00) Pacific Time (US & Canada)" but in application the timezone differs from the client system it shows as "(UTC-08:00) Baja California".
And importantly DST changes are not reflecting when I convert the UTC to Local. TimeZoneInfo.ConvertTimeFromUtc(DateTime, clientTimezone);
Note: I'm not storing Timezone information of client in database or anywhere. So everytime if a user enters the application, the application will recognize the timezone and it will react according to it.
My question is:
Whether the TimeZoneInfo class can work automatically work according to the adjusment rule, when we convert from UTC to Local?
Do we have to detect the DST for particular datetime using the method TimeZoneInfoObject.IsDaylightSavingTime(DateTime) and do conversion?
Is there any other classes in .Net which can sync with windows timezones?
A few things you should understand:
A time zone is not the same as a time zone offset. One cannot just take the number -8 and assume that the time zone should be Pacific time.
Offsets can change within a single time zone. For example, Pacific Time usually uses -8, but switches to -7 when daylight saving time is in effect.
The offsets in the DisplayName property of a TimeZoneInfo are only the standard offset. They match with the BaseOffset property. They do not change to reflect the current offset.
Time zone detection in JavaScript is imperfect. There are only three approaches:
Using the getTimezoneOffset function of the Date class, which should return you the offset of the date it was called on. For example new Date().getTimezoneOffset() gives you the current offset. With this approach, you should also be aware that there is a bug in the ES5 spec that can cause the wrong offset to sometimes be returned when called on older dates.
Using a library such as jsTimezoneDetect, which makes several calls to the getTimezoneOffset to attempt to guess at an IANA time zone identifier. The guess is suitable to set a default time zone when a list of time zones is presented to the user. It is just a guess, and could be wrong. If you want to use it on the back end with .NET, you'll need Noda Time, since TimeZoneInfo doesn't currently support IANA time zones. (You can optionally convert to Windows time zones if desired).
Some newer browsers support the ECMAScript Internationalization API, which has an optionally implemented function to return the time zone. It may work in some browsers, but is not guaranteed to return a valid result everywhere.
Intl.DateTimeFormat().resolvedOptions().timeZone
Again, you'll need Noda Time on the back end.
You said:
The problem is, if when I change timezone of client machine to (UTC -8:00), the client machine shows the timezone name as "(UTC-08:00) Pacific Time (US & Canada)" but in application the timezone differs from the client system it shows as "(UTC-08:00) Baja California".
This is probably related to how you are choosing a time zone in your application code. It sounds to me like you're scanning the list of server time zones and choosing the first one that matches some criteria. Since both of these time zones have the same base offset, you're probably just picking the wrong one, and you shouldn't be doing that anyway. But since you didn't show that part of your code, I can't help you much there.
To answer your specific questions:
Whether the TimeZoneInfo class can work automatically work according to the adjusment rule, when we convert from UTC to Local?
Yes, it can. There's nothing wrong with TimeZoneInfo, it's all about how you're using it. You probably are selecting the wrong time zone.
Do we have to detect the DST for particular datetime using the method TimeZoneInfoObject.IsDaylightSavingTime(DateTime) and do conversion?
No, you should not have to do that just to convert from UTC to a specific time zone. The ConvertTimeFromUtc function will handle that for you.
Is there any other classes in .Net which can sync with windows timezones?
TimeZoneInfo is the only one built in to the .NET Framework. Noda Time is a great alternative that can work with either Windows time zone or IANA time zones.
Lastly, I'll re-iterate what Jon said in comments. If all you're doing is displaying a particular instant in time to an end-user, then forget about time zone detection or working with local time on the server at all. Just send the UTC time to the client, and use either the UTC functions on the JavaScript Date object, or use a library like moment.js. Either can work in both UTC and local, and can convert between them. For example (using moment.js):
var valueFromServer = "2015-07-26T12:00:00Z"; // the Z means UTC
var localTime = moment(valueFromServer).format(); // "2015-07-26T05:00:00-07:00" (Pacific)
I'm currently working on a project that requires a user (in their respective time zone) to set a 'cut off' time for certain Notifications that they receive throughout the day. The user will, for instance, say they want no alerts prior to 8:00 AM and no later than 7:30 PM. This user is located in CST (the time zone information for each user is saved) and the 'server' is in EST. The server is where all of the logical decisions occur for which user should be notified, etc.
What would be the best practice to convert the time part only for comparison purposes?
My current thought would be to take the time set by the user, say "7:00 AM", and create a full DateTime object and store that as .ToUniversalTime(). On the server I can convert the DateTime object to Local time and compare the Time portion only.
Does anyone have a 'better' solution or possibly any advice from someone who has tackled a similar issue?
Thanks!
I suggest that you store the minimum time and maximum time as local times, without dates. You will also want to store the users general timezone information, for example "Central Time", not CST or CDT.
When you are ready to make a determination about sending a notification, convert the current UTC time to the user's local timezone and compare the stored time range against the converted time.
Trying to create a full calendar date from stored time information will be problematic in certain cases, specifically for daylight savings changes. By converting from UTC to user's local time for the comparison, that problem will be avoided.
How does the conversion to UTC from the standard DateTime format work?
More specifically, if I create a DateTime object in one time zone and then switch to another time zone and run ToUniversalTime() on it, how does it know the conversion was done correctly and that the time is still accurately represented?
There is no implicit timezone attached to a DateTime object. If you run ToUniversalTime() on it, it uses the timezone of the context that the code is running in.
For example, if I create a DateTime from the epoch of 1/1/1970, it gives me the same DateTime object no matter where in the world I am.
If I run ToUniversalTime() on it when I'm running the code in Greenwich, then I get the same time. If I do it while I live in Vancouver, then I get an offset DateTime object of -8 hours.
This is why it's important to store time related information in your database as UTC times when you need to do any kind of date conversion or localization. Consider if your codebase got moved to a server facility in another timezone ;)
Edit: note from Joel's answer - DateTime objects by default are typed as DateTimeKind.Local. If you parse a date and set it as DateTimeKind.Utc, then ToUniversalTime() performs no conversion.
And here's an article on "Best Practices Coding with Date Times", and an article on Converting DateTimes with .Net.
Firstly, it checks whether the Kind of the DateTime is known to be UTC already. If so, it returns the same value.
Otherwise, it's assumed to be a local time - that's local to the computer it's running on, and in particular in the time zone that the computer was using when some private property was first lazily initialized. That means if you change the time zone after your application was started, there's a good chance it will still be using the old one.
The time zone contains enough information to convert a local time to a UTC time or vice versa, although there are times that that's ambiguous or invalid. (There are local times which occur twice, and local times which never occur due to daylight saving time.) The rules for handling these cases are specified in the documentation:
If the date and time instance value is
an ambiguous time, this method assumes
that it is a standard time. (An
ambiguous time is one that can map
either to a standard time or to a
daylight saving time in the local time
zone) If the date and time instance
value is an invalid time, this method
simply subtracts the local time from
the local time zone's UTC offset to
return UTC. (An invalid time is one
that does not exist because of the
application of daylight saving time
adjustment rules.)
The returned value will have a Kind of DateTimeKind.Utc, so if you call ToUniveralTime on that it won't apply the offset again. (This is a vast improvement over .NET 1.1!)
If you want a non-local time zone, you should use TimeZoneInfo which was introduced in .NET 3.5 (there are hacky solutions for earlier versions, but they're not nice). To represent an instant in time, you should consider using DateTimeOffset which was introduced in .NET 2.0SP1, .NET3.0SP1 and .NET 3.5. However, that still doesn't have an actual time zone associated with it - just an offset from UTC. That means you don't know what local time will be one hour later, for example - the DST rules can vary between time zones which happened to use the same offset for that particular instant. TimeZoneInfo is designed to take historical and future rules into account, as opposed to TimeZone which is somewhat simplistic.
Basically the support in .NET 3.5 is a lot better than it was, but still leaves something to be desired for proper calendar arithmetic. Anyone fancy porting Joda Time to .NET? ;)
What #womp said, with the addition that it checks the DateTime's Kind property to see if it might already be a UTC date.
DateTime.ToUniversalTime removes the timezone offset of the local timezone to normalize a DateTime to UTC. If you then use DateTime.ToLocalTime on the normalized value in another timezone, the timezone offset of that timezone will be added to the normalized value for correct representation in that timezone.