LINQ选择所有项目，而不是从'where'

本文关键字：where 选择 项目 LINQ | 更新日期: 2023-09-27 18:05:53

我有一个Student对象列表，包含Id, FirstName和LastName。

我有一份迟到学生的学号列表。我想用LINQ查询找到迟到的学生的名字。

但是，我的代码没有返回请求的名称。它返回每个数字的所有学生的名字

我不知道我的linq查询出了什么问题

foreach (string studentnumber in pNumbers)
{
    MessageBox.Show(studentnumber);
    int snumber = Int32.Parse(studentnumber);
    //var studentNames = from student in students where student.Id == snumber select new { FirstName = student.FirstName, LastName = student.LastName };
    var studentNames = from student in students where student.Id == snumber select new { FirstName = student.FirstName, LastName = student.LastName };
    foreach (var s in studentNames)
    {
        string name = s.FirstName + " " + s.LastName;                        
        presentNamesList.Add(name);
    }

LINQ选择所有项目，而不是从'where'

下面是我如何做的一个例子

List<student> students = new List<student>();
students.Add(new student(1,"John","Doe"));
students.Add(new student(2,"Foo","Fighter"));
students.Add(new student(3,"Bob","Builder"));
students.Add(new student(4,"jack","ninja"));
List<int> nothere = new List<int>() { 2, 4 };
var present = students.Where(x => !nothere.Contains(x.studentid)).ToList();

列表present现在应该包含不在nothere列表中的学生

你可以这样做:

foreach (string studentnumber in pNumbers)
{
    int snumber = Int32.Parse(studentnumber);
    foreach(var s in students.Where(s=>s.Id == snumber))
    { 
       presentNamesList.Add(s.FirstName + " " + s.LastName);
    }
}
编辑:

一个班轮: 

presentNamesList.AddRange(students.Where(s=>!pNumbers.Contains(s.Id.ToString())).Select(s.Firstname + " " + s.Lastname).Select(s1=>s1.FirstName + " " + s1.LastName).ToList())
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