如何检查默认的DateTime值？

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

我需要检查DateTime值是否有值。

I have several options:

我有几个选择：

if (dateTime == default(DateTime))

要么

if (dateTime == DateTime.MinValue)

or using a nullable DateTime?

或使用可空的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.

我个人更喜欢第三个版本，因为它的可读性非常好。但是在我们的数据库中，我们有一些datetime列，它们被定义为非null。所以在某些情况下我必须选择前两个选项。

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.

我在某处读到了使用泛型时应该使用default关键字，但在这种情况下是不是更具可读性？当使用第二个选项时，我必须知道新的和空的DateTime实例的默认值是DateTime.MinValue，它具有我的实现细节的气味。

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

那么我应该使用哪个选项来使用“最佳实践”？

4 个解决方案

#1

I would probably make this really explicit:

我可能会说这个非常明确：

// 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.

好吧，所以我的名字稍微不那么罗嗦了，但你明白我的意思。如何初始化该值并不重要 - 很明显您正在尝试做什么。

(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.)

（当然，在任何时候都可以使用可空类型。我假设问题被问到，因为在某些情况下你不能这样做。）

#2

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

我需要检查DateTime值是否有值。

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

你已经非常多地描述了需要Nullable 的教科书情况。我会选择那个选项。

(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.)

（如果你需要将值保存到非空的db列，你显然需要某种转换层，但我会尽量保持任何“魔法”值尽可能接近db，并尽量保持你的C＃代码干净且惯用。）

#3

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

“最佳”做法是使用可以为空的DateTime。由于不信任“魔术”数字的原因，创建了可以为空的值类型。

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

这种方法最重要的是它的意图 - 在你的上下文中具有“默认”日期/时间意味着什么？

#4

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

也许您可以使用getdate（）在数据库中设置默认值，然后将所有空值更新为最小值或任何您喜欢的值。至少你会有一个条件

#1