How to check for default DateTime value?

Question

I need to check a DateTime value if it has a value or not.

I have several options:

if (dateTime == default(DateTime)) 

or

if (dateTime == DateTime.MinValue) 

or using a nullable DateTime?

if (nullableDateTime.HasValue) 

Personally I would prefer the third version, since its pretty good readable. But in our database we have some datetime columns which are defined as not null. So in some cases I have to go with the first two options.

I read somewhere that the default keyword should be used when working with generics, but isn't it much more readable in this case? When using the second option I have to know that the default value of a new and empty DateTime instance is DateTime.MinValue which has the smell of an implementation detail for me.

So which option should I use to use "best practice"?

Answer 1

I would probably make this really explicit:

// Or private, or maybe even public internal static readonly DateTime MagicValueForNullDateTimeInNonNullableColumns     = DateTime.MinValue; 

Okay, so I'd make the name slightly less wordy, but you get what I mean. It doesn't really matter much how you initialize that value - it's clear what you're trying to do.

(Of course, use a nullable type any time you can for this. I'm assuming the question was asked because you couldn't do so in certain situations.)

Answer 2

I need to check a DateTime value if it has a value or not.

You've pretty-much described the textbook situation requiring a Nullable<DateTime>. I'd go with that option.

(You'd obviously need some sort of translation layer if you need to persist the values to a non-null db column, but I'd try to keep any "magic" value as close to the db as possible, and try to keep your C# code clean and idiomatic.)