C# 在orderby中使用两个可为null的属性时，是否需要进行null检查？

我有一个包含两个属性的列表，Lastname和Firstname。它们可以为空，并且应该为空

这是我的代码行：

return memberlist.OrderBy(x => x.LastName).ThenBy(x => x.Firstname);

我的问题是，如果Lastname为null，它会运行ThenBy（）吗？否则我需要创建一个null检查？我想确保它按Lastname排序，如果为null，则按Firstname排序

假设我有一个如下列表：

var data = new List<Member>
{
    new Member { FirstName = "null", LastName = "A" },
    new Member { FirstName = "B", LastName = null },
    new Member { FirstName = "A", LastName = null },
    new Member { FirstName = null , LastName = "B" },
    new Member { FirstName = "A" , LastName = "B" },
    new Member { FirstName = "B" , LastName = "A" },
};

A
A
A
B
B
B

var result = data.OrderBy(x => x.LastName).ThenBy(x => x.FirstName);

---

是的，它将运行

ThenBy（）

基本上，所有具有

null

LastName

属性的项目都将按

FirstName

排序

OrderBy（）

将

null

值放在非null值之前

在以下示例中，

result

按声明的顺序返回项目：

var data = new List<Member>
{
    new Member { FirstName = "A", LastName = null },
    new Member { FirstName = "B", LastName = null },
    new Member { FirstName = "A", LastName = "NotNull" },
    new Member { FirstName = "B", LastName = "NotNull" }
};

var result = data.OrderBy(x => x.LastName).ThenBy(x => x.FirstName);

---

你试过了吗？在成员列表中插入null应该不会太难……但是如果我想要A、A、B、B而不是A、B、A、B呢？在这种情况下，

data.OrderBy（x=>x.FirstName）。然后是by（x=>x.LastName）

可以展开您的问题，给出一个具有所需输出的示例输入吗？然后我可以进行适当的编辑。

var result = data.OrderBy(x => string.IsNullOrWhiteSpace(x.LastName) ? x.FirstName : x.LastName)
                 .ThenBy(x => x.FirstName)