Linq to SQL DateTime values are local (Kind=Unspecified)
Isn't there a (simple) way to tell Linq To SQL classes that a particular DateTime property should be considered as UTC (ie having the Kind property of the DateTime type to be Utc by default), or is there a 'clean' workaround?
The time zone on my app-server is not the same as the SQL 2005 Server (cannot change any), and none is UTC. When I persist a property of type DateTime to the dB I use the UTC value (so the value in the db column is UTC), but when I read the values back (using Linq To SQL) I get the .Kind property of the DateTime value to be 'Unspecified'.
The problem is that when I 'convert' it to UTC it is 4 hours off. This also means that when it is serialized it it ends up on the client side with a 4 hour wrong offset (since it is serialized using the UTC).
The generated LinqToSql code provides extensibility points, so you can set values when the objects are loaded.
The key is to create a partial class which extends the generated class, and then implement the OnLoaded partial method.
For instance, let's say your class is Person , so you have a generated partial Person class in Blah.designer.cs .
Extend the partial class by creating a new class (must be in a different file), as follows:
public partial class Person {
partial void OnLoaded() {
this._BirthDate = DateTime.SpecifyKind(this._BirthDate, DateTimeKind.Utc);
}
}
SQL Server DateTime does not include any timezone or DateTimeKind information, therefore DateTime values retrieved from the database correctly have Kind = DateTimeKind.Unspecified.
If you want to make these times UTC, you should 'convert' them as follows:
DateTime utcDateTime = new DateTime(databaseDateTime.Ticks, DateTimeKind.Utc);
or the equivalent:
DateTime utcDateTime = DateTime.SpecifyKind(databaseDateTime, DateTimeKind.Utc);
I assume your problem is that you are attempting to convert them as follows:
DateTime utcDateTime = databaseDateTime.ToUniversalTime();
This may appear reasonable at first glance, but according to the MSDN documentation for DateTime.ToUniversalTime, when converting a DateTime whose Kind is Unspecified:
The current DateTime object is assumed to be a local time, and the conversion is performed as if Kind were Local.
This behavior is necessary for backwards compatibility with .NET 1.x, which didn't have a DateTime.Kind property.
我能想到做到这一点的唯一方法是在一个部分类中添加一个shim属性来完成翻译...
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