When Would You Prefer DateTime Over DateTimeOffset

Question

A few months ago I was introduced to the new DateTimeOffset type and was glad DateTime's flaws with regard to time zones were finally taken care of.

However, I was left wondering if there were any overhead or problems that could occur from using this new type.

I work on a multi-locale web application. Does anyone know of anything that could sway me from just using it for all my date/time work? Is there a window for abuse here?

Reference: DateTimeOffset: A New DateTime Structure in .NET 3.5 by Justin Van Patten

Tomb

Related question - #2533229 – Schutzstaffel

See also this answer – Ruyle

Does this answer your question? DateTime vs DateTimeOffset – Curet

That link doesn't take me to the article. This one does: learn.microsoft.com/en-us/archive/blogs/bclteam/… – Subtropics

Answer 1

Sometimes you really just want to represent a "local" (timezone unaware) date and time rather than an instant in time. To be honest it's more often useful to represent just a time - e.g. "wake me up at 8am, regardless of timezone" - but date and time could be useful too.

I agree that for the vast majority of cases, DateTimeOffset is a better fit. It does strike me as odd that there isn't a DateTimeTimeZone struct which has both the instant and its timezone though... an offset doesn't actually give you all the information you need. (For instance, given a DateTimeOffset, you don't know what the time will be 24 hours later, because you don't know when DST might kick in.)

If you want that kind of structure, I have a very crude implementation in another answer. I'm sure it could be improved very easily :)

Vodka

You could always represent your times in UTC and convert to a specific time zone when needed... – Tomb

Omer: But often you want to preserve the timezone information as well, I find. Yes, often you can get away with just the UTC time, but for recurrent events and the like you need to know the timezone too. – Vodka

Local time should usually only be used for future dates, where you want them to adjust with timezone changes. Historical data should always be stored in a consistent time zone, probably UTC though there may be historical reasons for another. (Example: for NYSE transactions data you might want EST across the board). – Odontoblast

@Ben: You're thinking about instants in time though. Not everything is like that. For example, "my birthday" is June 19th, every year - past, present and future. Or "the first day of the year 2000", which started at a different instant in each time zone. Or "6am" of my alarm clock. Basically it's worth making sure you know what kind of thing you're really representing. – Vodka

Answer 2

Well, one obvious answer would be when you need to support clients without the SP that it ships in (it isn't actually in 3.5 - it is in 2.0 SP1, which shipped at the same time).

Quotient

True, but I was actually talking about internally in my code and in the UI layer. – Tomb

Fair enough. I thought I'd mention it because VS multi-targetting doesn't make it obvious when you've used SP1 features while allegedly targetting 2.0. There is now an FxCop (etc) add-in to do this, at least. – Quotient

Answer 3

Whilst I wouldn't PREFER to use DateTime over DateTimeOffset, please note that sometimes you NEED to, as MS .Net does not support DateTimeOffset as a DataColumn.DataType property DataColumn.DataType Property even though SQL datetimeoffset has been around since SQL2008.

I myself had a problem with reading (ReadXml) a DateTimeOffset value of an XML exported DataSet with XmlReadMode.InferTypedSchema; it read it as a DateTime and crashed when I tried to merge it into a DateTimeOffset column

Lurlinelusa