具有可空DateTime的Linq表达式 [英] Linq expression with nullable DateTime

问题描述

我想查询一个可为空的DateTime的实体，例如，选择2005年制造的所有Cars:

I would like to query an entity with a nullable DateTime, for example, select all Cars built in 2005:

public class Car() {
    public int Id {get; set;}
    public DateTime? DateBuilt {get; set;}
    ...
}

我的Linq表达式通常看起来像这样:

My Linq-expression would normally look something like this:

int carsIn2005 = context.Cars.Count(x => x.DateBuilt.Year == "2005");

但是我不能使用.Year，因为Date是可为空的.我已经在Google上搜索了一下，找到了一些关于合并运算符的信息，但是无法从中获得一些有用的信息.如果Linq了解以下内容，那就很酷了:

But I cannot use .Year because the Date is nullable. I've googled a bit, found something about the coalescing-operator, but could not make something usefull from that. Cool would be if Linq understood the following:

int carsIn2005 = context.Cars.Count(x => x.DateBuilt.HasValue && x.DateBuilt.Year == "2005");

如果DateBuilt！= null，那么我应该可以将其视为DateTime.

If DateBuilt != null then I should be able to treat it as a DateTime.

推荐答案

尝试一下

int carsIn2005 = context.Cars.Count(x => x.DateBuilt != null && x.DateBuilt.Value.Year == 2005);

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