Question

我有一个学生对象列表，其中包含Id，FirstName和LastName。

我有一份学生身份列表，这些学生已经太晚了。我想找一些LINQ查询已经太晚的学生的名字。

但我的代码不会返回请求的名称。它返回每个学生的所有学生姓名

我无法弄清楚我的linq查询有什么问题。

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);
    }

Answer 1

以下是我将如何做到这一点的例子

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

Answer 2

您可以使用：

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);
    }
}

修改单线：

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

LINQ选择所有项目而不是从'where'请求

2 个答案: