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Reputation: 2966

How to check for default DateTime value?

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"?

Upvotes: 72

Views: 137380

Answers (4)

Jon Skeet
Jon Skeet

Reputation: 1500675

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.)

Upvotes: 84

Kuzgun
Kuzgun

Reputation: 4737

Maybe you can set a default value in your database with getdate() and then update all null values to min value or whatever you like. At least you will have one condition

Upvotes: 0

Igal Tabachnik
Igal Tabachnik

Reputation: 31548

The "best" practice would be using the nullable DateTime. Nullable value types were created exactly for that reason of not trusting "magic" numbers.

What's most important about this approach is its intent - what does it mean in your context to have a "default" date/time?

Upvotes: 9

LukeH
LukeH

Reputation: 269388

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.)

Upvotes: 20

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