linq 选择中的条件

Question

我在 2 个表之间有一个内部 linq 连接，如下所示：

(from A in table1 join B in table2 
on   A.name equals B.name 
where {some condition}
select new { 
A.name ,
A.color,
.
.
.
}).toList();

问题是在某些记录中 "name" 是 null 并且我希望 linq 查询在选择部分用“”替换 null .

类似这样的：

select new {
A.name!=null?A.name : " "
.
.
.
}

我该怎么做？

（我知道我可以在 where 中有一个条件，我检查不是 null 但在这种情况下它将跳过该记录但我想取它并替换null 名称和字符串）

提前致谢；）

Answer 1

您可以使用带有空字符串的null-coalescing operator ?? 作为默认值。然后将其结果分配给匿名类型的属性

select new { 
    name = A.name ?? "",
    //rest of code
}

Answer 2

Sample

using System;
using System.Linq;
using System.Collections.Generic;


public class Program
{
    public static void Main()
    {
        // Student collection
        IList<Student> studentList = new List<Student>() { 
                new Student() { StudentID = 1, StudentName = null, Age = 13} ,
                new Student() { StudentID = 2, StudentName = "Moin",  Age = 21 } ,
                new Student() { StudentID = 3, StudentName = "Bill",  Age = 18 } ,
                new Student() { StudentID = 4, StudentName = "Ram" , Age = 20} ,
                new Student() { StudentID = 5, StudentName = "Ron" , Age = 15 } 
            };

        // LINQ Query Syntax to find out teenager students
        var teenAgerStudent = (from s in studentList
                              where s.Age > 12 && s.Age < 20
                              select new {Name=s.StudentName??"Tuna"}).ToList();

        Console.WriteLine("Teen age Students:");

        foreach(var std in teenAgerStudent){            
            Console.WriteLine(std.Name);
        }
    }
}

public class Student{

    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public int Age { get; set; }

}