I've been searching a lot but couldn't find a solution. How do you deal with a DateTime that should be able to contain an uninitialized value (equivalent to null)? I have a class which might have a DateTime property value set or not. I was thinking of initializing the property holder to DateTime.MinValue, which then could easily be checked. I guess this is a quite common question, how do you do that?
+32
A:
For normal DateTimes, if you don't initialize them at all then they will match DateTime.MinValue, because it is a value type rather than a reference type.
You can also use a nullable DateTime, like this:
DateTime? MyNullableDate;
Or the longer form:
Nullable<DateTime> MyNullableDate;
Joel Coehoorn
2008-10-21 12:56:04
It would greatly help if you provide an example of how to use it. How do you assign the DateTime in the database, which could be DBNull, to the nullable DateTime?
kirk.burleson
2010-08-13 13:29:41
+3
A:
I'd consider using a nullable types.
DateTime? myDate instead of DateTime myDate;
David Mohundro
2008-10-21 12:56:11
+12
A:
If you're using .NET 2.0 you can use the nullable type:
DateTime? dt = null;
or
Nullable<DateTime> dt = null;
then later:
dt = new DateTime();
And you can check the value with:
if (dt.ContainsValue)
{
// Do something with dt.Value
}
Or you can use it like:
DateTime dt2 = dt ?? DateTime.MinValue;
You can read more here:
http://msdn.microsoft.com/en-us/library/b3h38hb0.aspx
Mark Ingram
2008-10-21 12:56:19
You can use nullable types even in earlier versions of .NET, no need for 3.0.
stephenbayer
2008-10-21 12:57:27
It came in .NET 2.0 right? The ? syntax was added to VB.NET in 3.5, but it has been in C# since 2.0 I believe.
David Mohundro
2008-10-21 12:58:25
Nullable types are available in .Net 2.0. C# has had the shorthand ? notation from 2.0. Only VB.Net didn't have the shorthand ? in 2.0 but you could use Nullable(Of DateTime)
Mendelt
2008-10-21 12:59:44
For the last snippet, I would say DateTime dt2 = dt ?? DateTime.MinValue;
Joel Coehoorn
2008-10-21 13:02:51
+1
A:
You can use a nullable class.
DateTime? date = new DateTime?();
Aaron Smith
2008-10-21 12:56:47
+3
A:
You can use a nullable DateTime for this.
Nullable<DateTime> myDateTime;
or the same thing written like this:
DateTime? myDateTime;
Patrik
2008-10-21 12:56:57
A:
I always set the time to DateTime.MinValue. This way I do not get any NullErrorException and I can compare it to a date that I know isn't set.
Daok
2008-10-21 12:57:16
That means you can't tell the difference between "I really need a DateTime here" and "It's optional" - Nullable<DateTime> is a much better solution, IMO.
Jon Skeet
2008-10-21 13:01:29
? I really do not get your comment. Yeah I know when the DateTime is so far aways of reality is like if it was null...
Daok
2008-10-21 13:03:10
I am just suggesting an other solution. Instead of repeating what have been suggested already 10 times here.
Daok
2008-10-21 13:04:48
I mean that your type system can't indicate the optional nature of the value.
Jon Skeet
2008-10-21 13:09:35
It is convenient, but I view DateTime.MinValue as a value, not a special case condition. It can only lead to problems down the line. I'd go with Nullable<DateTime>.
spoulson
2008-10-21 13:13:50
There are any number of bad designs which won't always cause problems - but shouldn't be recommended anyway. I could come along and say that I make all members of all types public, and haven't had any problems - would that be good advice?
Jon Skeet
2008-10-21 13:22:49
I think you miss something about my answer, Spoulson wrote something and I was answering. About public members, well it's not the same and you know it. it's like String.Empty or null. You can do both, not because String.Empty is better that null is wrong. What ever.
Daok
2008-10-23 17:22:29
I'm with Daok on this. It might not be the "by the book" approach but it's better than getting a NullReferenceException or dealing with the cumbersome Nullable type. Besides, how many applications are out there that actually need to reference the date January 1, 1 A.D.?
Repo Man
2010-03-29 18:15:55
+1
A:
You can set the DateTime to Nullable. By default DateTime is not nullable. You can make it nullable in a couple of ways. Using a question mark after the type DateTime? myTime or using the generic style Nullable. I have added a couple of links on msdn.
A:
myclass.MyNullableDateTime = (drOrder["Field1"] == DBNull.Value) ? (DateTime?)null : ((DateTime)drOrder["Field1"]);
imanabidi
2010-04-28 16:08:16