Automatic timezone conversion in .NET web services

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Hi All,

When we pass a DateTime data type to a .NET web service or when data is returned in a DataTable back to the client, all the DateTime fields are converted to match the destination timezone. For example, if the server runs in Eastern Time (GMT-5) and the Client runs in Indian Time (GMT+5:30), and we pass 6:00 PM to the server, the time is reflected at the server as 7:30 AM. Whereas this is okay in most situations because both times represent the same point in time, it is highly undesirable when we want to make a comparisons with a field in the database, etc. One solution I have come across on googling this is storing values as UTC in database, but this is not practical when we integrate web service into existing systems. I have my own ways of dealing with this issue (using some time functions, etc,), but i would like to know if there is something built into .NET (preferably .NET 2.0) to get around with this.

Thanks in advance

Posted 24-Jan-11 4:03am

Nejimon CR

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Richard MacCutchan · Answer 1 · 2011-01-24T04:13:00

Solution 1

You should always store time values as UTC. There is absolutely no reason why you would ever need to store them as anything else. Only in that way can you be sure that the value can be displayed correctly for any user, in any part of the world.

Posted 24-Jan-11 4:13am

Richard MacCutchan

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Nejimon CR 24-Jan-11 10:35am

Hi Richard,
It makes sense if we are building a project from scratch. I have a database where more than 100,000 records already and it is growing. The database is accessed by applications locally on the server via network as well as people from outside via web service. It is not practical to write them to database again.

Furthermore, even if you store them in database as UTC, when a particular record is retrieved and sent to the client in a DataTable, the date will get converted by 10:30 hours at the client (which is apparently wrong).

Richard MacCutchan 24-Jan-11 10:54am

OK, you already have the data so you are stuck.
I don't understand the second paragraph; what do you mean "data will get converted by 10:30 hours at the client"?

Nejimon CR 24-Jan-11 11:11am

My database is MS Access. The original data contains two date fields. The client applications (desktop applications) request data between two dates (say 01/10/2011 and 01/20/2011). At server, a web method retrieves the qualified records and sends them to the client in a data table. Suppose one of the rows in the data table originally contains a date 01/11/2011 7:30 AM, which is retrieved from database. The original data in database contains no timezone information. When this data reaches the client, ideally it should reflect the same time, right because the database contains that value and no reason to convert to any other timezone. But when this field reaches the client, the client sees the time as 01/11/2011 6:00 PM (because my server-client time difference is 10:30 hours). The end user thinks that the original data was 6:00 PM whereas the original data in the database is only 7:30 AM.

Richard MacCutchan 24-Jan-11 11:48am

Well that's all fine as long as all your clients are in the same timezone.

Nejimon CR 24-Jan-11 11:21am

The main thing I need to know is this: Is there any way to send/receive DateTime fields to and from web service without them being converted at the other end (whatever sent is reflected at the other end too, more or less like a string)?

Richard MacCutchan 24-Jan-11 11:49am

Send it as a string and it should stay the same.

Nejimon CR 24-Jan-11 12:07pm

Yeah, I can do that for whatever DateTime parameters I send to the web service, but no way to do the same on a data table returned from the server. Currently I use the following code, where two DateTimePickers are used to specify the From/To dates:

Dim DateFrom As Date = dtpDateFrom.Value.Date 'to strip the time value and make it from 12:00 AM
Dim DateTo As Date = dtpDateTo.Value.Date.Add(New TimeSpan(23, 59, 59)) 'until just before midnight of to-date.

Dim Diff1 As TimeSpan = DateFrom.Subtract(DateFrom.ToUniversalTime)
DateFrom = DateFrom.ToUniversalTime.Add(Diff1)

Dim Diff2 As TimeSpan = DateTo.Subtract(DateTo.ToUniversalTime)
DateTo = DateTo.ToUniversalTime.Add(Diff2)

'now call the web method. this way, exactly the same time that is sent will be reflected on the server (even if the clients are from different timezones):

Dim Dt as DataTable=Svc.GetDataFromServer(DateFrom, DateTo)

Similarly, I convert the time in returned Datatable to UTC and subtract the difference between Server time and UTC from the time in Datatable.

This works fine for all practical purposes, but the whole idea of my question was if there is something simpler built into .net itself to avoid this overhead

Richard MacCutchan 24-Jan-11 12:22pm

I think your solution is probably the best option there is, given the way your date/time values are stored.

Nejimon CR 24-Jan-11 12:09pm

Thank you, Richard, for sharing your ideas with me...

Nejimon CR 24-Jan-11 13:04pm

After a bit of researching, I have found out that there is something built into .net already. They are:
'to send data to web service timezone independently
YourDateVariable=Date.SpecifyKind(YourDateVariable, DateTimeKind.Unspecified)

'to send data from web service timezone independently
YourDatatable.Columns("YourFieldName").DateTimeMode = DataSetDateTime.Unspecified

rpraetorius 27-Mar-12 13:34pm

In general, I agree with the idea that all times should be stored and transmitted in UTC, converted from and to the user's time zone when entered and displayed. This can't be repeated too many times.

The problem is .NET's lack of a Date type. Something that's a date with no time in a database comes through as midnight on the morning of the day in question. When this goes in to a DateTime variable and .NET starts doing helpful time zone calculations on it, it's not really being helpful.

If you have control of the XSD, of course, you can make something a Date rather than a DateTime, since XSDs know about the difference. But that can be kind of awkward when dealing with DataTables, which are all about the convenience.

The DateTimeMode solution has been around since .NET 2.0 (although surfing indicates that it had some implementation problems when it was first done), but for some reason it takes considerable persistence to find it. I wish it would show up earlier in searches.

Finally, a small pet peeve. They said it better at Wikipedia than I would, so I'll just post the link.

Richard MacCutchan 28-Mar-12 4:08am

The original question refers to an issue with a DateTime, so while your comments are valid they are not really relevant to this issue.

rpraetorius · Answer 2 · 2012-03-27T07:21:00

Solution 2

http://stackoverflow.com/a/6935884/ has the best answer I've seen. DataColumn has a DateTimeMode member. If you change it from UnspecifiedLocal (the default?) to Unspecified, .NET quits sending the time zone. This works great for us. YMMV

Posted 27-Mar-12 7:21am

rpraetorius

Comments

Ajit Kumar Nayak 8-Nov-16 1:08am

it works for me. thanks