C#林克加入查询

本文关键字：查询 林克 | 更新日期: 2023-09-27 17:57:37

我正在尝试创建一个查询，将ID和StudentID字段中的Student和Enrolled数据连接起来，这样我就可以只显示在History中注册的学生的姓名，因为Steve Thomas的ID是3，History所需的StudentID也是。

我的另一个查询（IEnumerable学生查询）只访问了学生数据，没有注册。因此，我不确定如何将两者结合在一起。我会使用多个from吗？

class Student
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int ID { get; set; }
    public DateTime DateOfBirth { get; set; }
}
class Enrolled
{
    public int StudentID { get; set; }
    public string CourseName { get; set; }
}

IEnumerable<Student> students = new List<Student>()
{
    new Student {FirstName = "Jim", LastName = "Smith", DateOfBirth = new DateTime(1990, 5, 21), ID = 1},
    new Student {FirstName = "Diane", LastName = "Sawyer", DateOfBirth = new DateTime(1992, 11, 1), ID = 2},
    new Student {FirstName = "Steve", LastName = "Thomas", DateOfBirth = new DateTime(1994, 4, 4), ID = 3},
    new Student {FirstName = "Pablo", LastName = "Dicaz", DateOfBirth = new DateTime(1973, 3, 30), ID = 4},
    new Student {FirstName = "Hannu", LastName = "Korppi", DateOfBirth = new DateTime(1988, 6, 16), ID = 5},
    new Student {FirstName = "Marie", LastName = "St. Claude", DateOfBirth = new DateTime(1982, 1, 19), ID = 6}
};

var enrolllist = new List<Enrolled>
{
    new Enrolled {CourseName = "Computer Science",StudentID = 2},
    new Enrolled {CourseName = "Computer Science",StudentID = 5},
    new Enrolled {CourseName = "History",StudentID = 1},
    new Enrolled {CourseName = "Psychology",StudentID = 2},
    new Enrolled {CourseName = "History",StudentID = 4},
    new Enrolled {CourseName = "Computer Science",StudentID = 3},
    new Enrolled {CourseName = "Psychology",StudentID = 6},
    new Enrolled {CourseName = "History",StudentID = 3},
};
IEnumerable<Student> query = from s in students
                             where s.DateOfBirth.Year < 1990
                             orderby s.FirstName
                             select s;
foreach (Student stud in query)
{
    Console.WriteLine(stud.FirstName);
    Console.ReadLine();
}

C#林克加入查询

您可以连接这两个集合，类似于在SQL查询中连接两个表的方式。

var query = (from s in students
             join e in enrolllist on s.ID equals e.StudentID
             where e.CourseName == "History"
             select s)

students.ID字段与enrolled.StudentID字段连接。

您可以在这里和这里阅读更多关于join如何工作的信息。

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