Sunday, 29 July 2012

WCF date time serialization

I just encountered a horrible problem where my WCF service was doing all the hard work calculating hourly volumes for long and short days with respect to Daylight Savings Time. Results were being returned as two properties, StartTimeLocal and StartTimeUtc.

My unit tests all worked fine.

But when the clients were consuming the service a problem was being encountered. The times were different and causing problems.

In the end I realised - because the DateTime was defaulting to DateTimeKind.Local, the client was taking the property named UTC, assuming it was local time and adjusting it!

The rule is - it is safest to return your DateTimes as DateTimeKind.Utc - that way the client will not make assumptions about timezone conversions.

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