I have MVC web application. I am storing UTC time in database. (Not datetime but just a time). In C# When I retrieve this time from the database I get timespan object back. I also have offset available in minutes. For example.
double offset = 600;
How do I use this offset to convert timespan to local datetime.
Note I don't want to use DateTime.ToLocalTime () method because that will use server's timezone.
UPDATE1
I am using the Javascript new Date().getTimezoneOffset() method to get the client's offset, and i have offset value stored on the server. Then I also have drop down list that show times as 12:00 AM, 12.30 AM, 1:00 AM etc etc. The dropdownlist is bound to model property SelectedDateTime of type DateTime. Idea is to convert user selected time to UTC and then UTC to localtime based on the offset. So lets say i have offset 300 minitues that would be 300/60 = 5 hours
double offset = 5.00; // this is available on the server
When the user selects time in a drop down list, I am getting a datetime object on the server, ignoring the date part i want to store UTC time into database. This is how I'm converting to UTC time.
TimeSpan utcTime = SelectedDateTime.AddHours(offset).TimeOfday;
I store this utcTime into the database. Now I want to convert UTC timespan into the client's datetime.
I am assuming i have Subtract offset now
var newLocalTimeSpan = utcTime.Subtract(TimeSpan.FromHours(offset));
var newLocalDateTime = new DateTime(newLocalTimeSpan.Ticks, DateTimeKind.Local);
However this throws the error:
Ticks must be between DateTime.MinValue.Ticks and
DateTime.MaxValue.Ticks.\r\nParameter name: ticks
For example with offest 5 hours, If user selects 8:00 PM then it will be converted to UTC and will be stored as 01:00:00.0000000 in database. When I retrieve the UTC value from database its '1:00:00 AM'. Then I subtract 5 hours form this TimeSpan which equals to `-4' now and if I pass Ticks to DateTime..i get above error.
NOTES: If you are curious why model property is DateTime instead of TimeSpan thats because i am using Kendo TimePicker which needs DateTime type.
UPDATE 2
I really appreciate all for your help. I have gone through all the articles #Matt Johnson has posted and it looks like I should not be using offset for calculating the UTC time. Mainly because of the day light time saving. But instead I should be using timezone. So I have 3 options here to find client’s time zone:
1> Use JavaScript to detect time zone
In JavaScript I can do new Date().toString() which returns date time as Sun May 22 2016 02:12:36 GMT-0500 (Central Daylight Time) I can then parse the string to get “Central Daylight Time” and post it to the server. However on server, for .net “Central Daylight Time” is not a valid windows time zone ID.
Question
Is this correct approach? Is JavaScript returning IANA zone id? Will it always return IANA zone id?
If JavaScript is returning IANA Id then I can use Matt’s article here to get windows time zone id
2> Use http://momentjs.com/ to detect client’s time zone
Question
Is momentjs returns IANA zone id?
If momentjs return IANA zone id then I can use Matt’s article above to get windows zone id. One of the reason I don’t like this approach is because I have to use 2 third party libraries momentjs and Noda Time
3> Provide user a drop down list using TimeZoneInfo.GetSystemTimeZones() and let the user selects the timezone.
User will select a time and timezone, then on server I will convert it to UTC using selected timezone and save it DB. However I have to show that time on some other pages, So I again need timezone. That means I have to put the drop down list in such a place on UI where it will be available all the time. Like top menu.
(I can certainly save timezone into DB along with the time, however if user travel to other place he will still see time in initially selected time zone. Which I don’t want)
Are these correct approaches? Am i missing something?
Question
Assume that I implement timezone selection using one of the approach above and i have correct client's time zone with windows timezone id on server in some variable.
Now lets say user selects 6:00 PM (Central Daylight Time , UTC -5) which will convert to UTC as 23:00:00. As long we are in Central Daylight Time the conversion from UTC to local will show 6:00 PM. Once we go into Central Standard Time which is UTC -6 Will the conversion still show 6:00 PM or 5:00 PM?
I am planning to use TimeZoneInfo.ConvertFromUtc(datetimevalue, timezone) method for converting UTC to Local
In general, there are only two viable approaches:
Pass only UTC dates and times to the client, and do all conversions to local time in the browser using JavaScript.
Use this approach when you don't care what the time zone actually is, but you just want it to match the browser's local time.
The Date object can do this, but you may find it easier to use a library such as moment.js, which gives you better control of output format, among other things.
Apply a time zone (not just an offset) to the UTC date and time on the server side, to produce the correct local time value.
Use this approach when the time zone affects an entire application, and needs to be known in server-side business logic.
You can try to guess the user's time zone using jsTimeZoneDetect or moment.tz.guess() in moment-timezone. However, it's just a guess, and it is always an IANA time zone ID (such as America/Los_Angeles).
Asking the user for their time zone from a list is a good idea. Usually one would place this on a user settings or profile page. You can use the guess made earlier to pick a default value from the list.
You will indeed need to use Noda Time on the server if you are using IANA time zones on the client.
Some applications choose to list Windows time zones instead, which is a much simpler approach as you can get everything from the TimeZoneInfo class. However, recognize that there are limitations with this approach including:
Localization issues, as you cannot easily get at display name strings other than the ones matching the operating system's default language, not .NET's globalization and localization features.
Maintainability issues, as you yield control to the operating system for keeping the time zone data updated. This may seem more convenient, but you may find that your hands are tied when keeping up with short-notice time zone changes. This is especially problematic when you don't have control over how or when updates are applied to the OS, such as with Microsoft Azure App Service.
Compatibility issues, as Windows time zones aren't generally recognized outside of Windows. If you ever expose the user's time zone setting in an API, you'll likely have translation issues for callers from other platforms.
Now, getting to your specific points:
I am using javascript new Date().getTimezoneOffset() method to get the client's offset...
That gives you the client's current offset. You have no guarantees that it is the correct time zone to apply for an arbitrary date and time.
If wanted to apply a fixed offset to a UTC DateTime in C#, the best way is with a DateTimeOffset.
DateTime utc = new DateTime(2016, 12, 31, 0, 0, 0, DateTimeKind.Utc);
DateTimeOffset dto = new DateTimeOffset(utc); // DateTimeKind matters here
TimeSpan offset = TimeSpan.FromMinutes(-300); // The offset is inverse of JavaScript's
DateTimeOffset result = dto.ToOffset(offset);
But do note this is only for a fixed time zone offset. For a true time zone, you would use the TimeZoneInfo class if you're using Windows time zones, or you would use NodaTime's DateTimeZone class for IANA time zones.
In JavaScript I can do new Date().toString() which returns date time as Sun May 22 2016 02:12:36 GMT-0500 (Central Daylight Time) I can then parse the string to get "Central Daylight Time" and post it to the server.
No, this approach is not recommended, for several reasons:
There's no guarantee you will get output in any particular format from JavaScript's toString function. The results are implementation specific, and will vary across browsers and platforms.
They are generally intended for display purposes. When DST is in effect, they'll show a daylight name, and when standard time is in effect they'll show a standard name.
They are often localized for the user's language, English, French, Chinese, etc.
The only native API that can return the user's time zone is:
Intl.DateTimeFormat().resolvedOptions().timeZone
This is part of the ECMAScript Internationalization API. Unfortunately, it currently only works in a handful of browsers. Both jsTimeZoneDetect and moment.tz.guess() will use this API if it's available, then will fall back to their own guessing logic if not.
Assume that i implement timezone selection using one of the approach above and i have correct client's time zone with windows timezone id on server in some variable. Now lets say user selects 6:00 PM (Central Daylight Time , UTC -5) which will convert to UTC as 23:00:00. As long we are in Central Daylight Time the conversion from UTC to local will show 6:00 PM. Once we go into Central Standard Time which is UTC -6 Will the conversion still show 6:00 PM or 5:00 PM?
I am planning to use TimeZoneInfo.ConvertFromUtc(datetimevalue, timezone) method for converting UTC to Local
As you said earlier, "Central Daylight Time" is not a valid Windows time zone identifier. Your user wouldn't pick that. You'd display a list generated from TimeZoneInfo.GetSystemTimeZones(), showing the DisplayName to the user, and using the Id for the value. The Id would be "Central Standard Time", which indeed is the correct identifier for US Central Time, inclusive of both CST and CDT - despite having the word "Standard" in the string.
You need to convert the TimeSpan to a DateTime, using the current Year, Month and Day. If you subtract from a TimeSpan without doing so, it can result in an unobtainable date.
Also, I noticed in your update that you left the results in a DateTime, so I did the same.
This code is showing you the time if the UTC time was 1:00 AM, as your problem states.
double offset = 5.00;
TimeSpan utcTime = new TimeSpan(1,0,0); //setting manually to your representation of 1 am.
DateTime newLocalDateTime = new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day, utcTime.Hours, utcTime.Minutes, utcTime.Seconds);
newLocalDateTime = newLocalDateTime.Subtract(TimeSpan.FromHours(offset));
Related
My scenario is a Date object created using the browser timezone (just using new Date()) and sent to the server, but I want to send this date with another specific timezone let's assume it's, Europe/Athens.
What would be the best representation of the actual date string so I can convert it back to a Date object in the backend in the actual Europe/Athens date?
I have the timezone info but not sure how to get a Fri Feb 05 2021 05:30:00 GMT-0500 (Eastern Standard Time) and convert it to Europe/Athens date.
I have tried to use date-fns but didn't get far.
You've got a few different questions and misconceptions, so I will attempt to address each of them, starting with question in the title:
How to convert a Date in specific Timezone and send to server
If you mean a date like 2021-01-18, that cannot be in a particular time zone. It is, by definition, just a date. Think about a printed calendar you might hang on your wall that has a square for each date. There are no time zones associated with such calendars. One can ask "what date is it now in a particular time zone", but the answer itself has no time zone.
If instead you meant a JavaScript Date object, the answer is again "you can't". The Date object is not actually a date, nor does it have a time zone, but rather it is a timestamp. Internally, a Date object only holds one value - the number of milliseconds that have elapsed since 1970-01-01 00:00:00.000 UTC (not considering leap seconds). It has no time zone. Instead, some functions such as .toString() will apply the system-local time zone while operating. That time zone comes from the operating system (in most cases). It is not stored inside the Date object itself.
My scenario is a Date object created using the browser timezone (just using new Date()) ...
That will use the system clock where the browser is running, but the time zone is not relevant. The Date object will be constructed from the Unix timestamp that represents "now". Such timestamps are inherently UTC based. The browser fetches the UTC time directly from the operating system, without considering time zone.
... and sent to the server
One cannot send an object to a server without going through deserialization on one side and serialization on the other.
... but I want to send this date with another specific timezone let's assume it's, Europe/Athens.
What would be the best representation of the actual date string so I can convert it back to a Date object in the backend in the actual Europe/Athens date?
Since the object only represents "now", you don't need to send it in a time zone specific format. Just send the UTC time. The ideal format is ISO 8601, which can be obtained directly using the .toISOString() function from the Date object.
Depending on your use case, you might also consider whether you might instead just take the UTC time from the server instead. At least you will have some control over the clock.
On the server side, if you need the time in a specific time zone, then convert from UTC to that time zone on the server, not on the client.
Also, from comments:
I believe even EPOCH is different between timezones. I could just get the EPOCh and then try to work with converting to specific timezones.
That is incorrect on a few levels. First, understand that epoch is just an English word meaning essentially "a representation of a starting point". It isn't a format, nor is it an acronym. In JavaScript, Date objects use Unix timestamps, which use an epoch of 1970-01-01T00:00:00.000Z. In other words, Midnight Jan 1st 1970 UTC is the 0 timestamp. Sometimes, such timestamps are referred to as "epoch time". That's a misnomer in my opinion, but even still - they are always UTC based. There is no time zone, and thus they are the same for the whole world.
Try to use toLocaleString:
let date = (new Date()).toLocaleString("en-US", {timeZone: "Europe/Athens"});
I have a date (in UTC milliseconds) that I am displaying on a page (AngularJS 1.4.0), and the users would like to see it in Eastern time, regardless of the time zone set on their computer.
I am using the date filter, and from the documentation I see
$filter('date')(date, format, timezone)
Timezone to be used for formatting. It understands UTC/GMT and the continental US time zone abbreviations, but for general use, use a time zone offset, for example, '+0430' (4 hours, 30 minutes east of the Greenwich meridian) If not specified, the timezone of the browser will be used.
Using timestamps from today, if I use something like
{{ record.Timestamp | date:'HH:mm:ss.sss':'EST' }}
it writes the time as I expect, but I think I'm going to be off by an hour when DST rolls around. I can also specify 'EDT' and it will bump the time ahead an hour, but is there a timezone abbreviation I could use that just means "Eastern", and uses the date itself to determine whether to use EST or EDT? Or am I going to need to inspect the date and create an offset myself: either -0500/EST or -0400/EDT, depending on the date? (and it looks like timezone can only be a string, not a function, so that's going to complicate my auto-detection).
It just seems unlikely that anyone would want to hard-code the display to either EST or EDT - it's much more likely that they want the time zone, adjusted for DST.
I would use Moment.js and Moment Timezone for this kind of stuff to get the right datetime. Filter in AngularJS is just to format the datetime object and show it in UI.
You can also use some ready to use directives like Angular-Moment.
It has got all sort of filtering available.
I know this seems like a straight forward question - but although Moment.js and moment timezone are very powerful tools for getting/setting and formatting dates..
I'm having an issue snapping my application to a single timezone.
What I want, is for a user to choose from a date/time picker - and to send that as a unix timestamp in UTC.. but the date/time picker MUST be considered to be BST.
In other words, even if you're using the site from abroad - the date/time you select should be the UTC value for if you had chosen it in the UK.
var local = moment(dateTime).unix();
var london = moment(dateTime).tz('Europe/London').unix();
var berlin = moment(dateTime).tz('Europe/Berlin').unix();
All 3 variables will equal the SAME UTC timestamp on the same machine, but a different timestamp on another machine running in a different timezone.
Think about it... if my date/time was 3pm on Saturday.. that's a DIFFERENT UTC in London than it is in Berlin, since it will occur one hour earlier in Berlin.
How do I force a date/time to be considered as a specific timezone?
Thanks :-)
Assuming dateTime is an ISO8601 string, and you want the date to be in the Europe/London timezone at all times all you need is:
moment.tz(dateTime, 'Europe/London').unix()
This tells moment to interpret that time as London time, provided that it does not have a specified offset. If it has an offset, it is going to convert from the time of the offset to London time.
So, for me in America/Chicago, you can see the effect of this:
//unix timestap in london time
moment.tz('2016-12-30', 'Europe/London').unix()
1483056000
//parse that timestamp back to my local time
moment.unix(1483056000).format()
"2016-12-29T18:00:00-06:00"
Keep in mind that London has multiple offsets due to Daylight Saving Time. I think this is what you want.
If you wanted it to always keep a fixed offset of +0, then you could just use UTC:
moment.utc(dateTime)
With dateObj.toISOString().slice(0, 19).replace('T', ' ') we can convert a date object to mysql datetime format in javascript. But the timezone is always considered as the client's (browser's) timezone.
I want to convert a date and time of different time-zones (not the browser's timezone) to UTC time and then to mysql time format.
Eg:
Alice is scheduling a meeting in New-York from Sydney. Alice enters New-York time as the input. Even thought the browser's location is Sydney, the javascript code has to assume the browser's location is in New-York and convert the date time to UTC, then to mysql format.
I can get current New-York time with, dateObj.toLocaleString('en-US', { timeZone: 'America/New_York'}). But not sure what to do next. Seems to be something to do considering time differences...
Anybody knows how to do this?
So you want to always store the date in the utc representation of where the event occurred.
To Save:
You know Alice has her Time Zone set to a specific value, therefore, you need to convert from Alice's time zone to UTC. If Alice entered 11:59:59 PM for the meeting time then the time stored would be when it occurred in GMT, which would be +4/5 hours depending on whether DST is being observed. It sounds like using your solution you would need a function like dateTimeUTC=FromSpecificTimeZoneToUTC(specificTimeZoneDateTime,'Eastern Standard Time')
dateObj.toLocaleString('en-US', { timeZone: '<TimeZone name for GMT>'})
To View:
Alice now has adjusted here Time Zone info to be in PST, which is GMT-8. Since we know the event occurred at 3:59:59 AM GMT we would need a function to convert from UTC back to a specific time, PST, this would yield 7:59:59 PM in Alices' changed config.
dateTimeSpecific=FromUTCToSpecificTimeZone(uTCTimeZoneDateTime,'Pacific Standard Time')
In my opionion you might be better served handling conversions like this on the server side where you have control over the tz info. I think a js might be too inconsistent because the time information is based on the client computers regional settings, not the preferred timezone of the operation. Plus, time zone info is subject to change. I don't know how js handles those changes.
I need to find the time zone of the client machine using ASP.NET (C#) or JavaScript. What are the different time zones that are available all over the world and how to convert the date and time based on the users time zone.
Please provide some suggestions or sample coding to change the time based on the time zone.
You cannot find client time zone settings from ASP.NET.
You can use JavaScript to tell the current time, but there are several time zones that can be synchronized at any given time.
In Chrome, you can get the time zone from the JavaScript date object. There's no specific function for it, from what I've found, but the code
(new Date()).toString()
will yield something like
Mon Apr 18 2011 08:58:59 GMT+0200 (W. Europe Daylight Time)
In websites, the best approach I've found has been to have a setting for each user to specify the time zone to display all times in. If the JavaScript getUtcOffset gives a different offset than what is expected for the user's time zone, I'll show a notice for the user to review their settings. If time zone can be guessed from the date (which I've only found to be the case in chrome), I'll suggest that time zone, but I still resort to a select box for the user to manually pick the time zone.
Even so, it is possible to have the wrong time zone setting, without the script noticing it, because for a great part of the year, the two time zones may be perfectly synchronized.
Once you have a time zone (you can enumerate them all with System.TimeZoneInfo.GetSystemTimeZones()), you can convert UTC dates with System.TimeZoneInfo.ConvertTimeFromUtc and System.TimeZoneInfo.ConverTimeToUtc, respectively.