Question

我有三个班级

class students
{
   int age
   string name
   List<Courses> Courses
}
class Courses
{
   int courses_id
   string Name
}
class Subject_Name
{
   string Name
}

我有一个学生列表和subject_names列表我想写一个linq查询，如果有任何返回这些学生单个科目与他们的课程匹配。

Sql查询就像

select * from students 
inner join Courses on students.Courses_id=Courses.Courses_id
and Courses.Name in (select name from subject_Name)

任何人都可以寻求帮助。

Answer 1

您需要执行以下操作：

string[] subject_names = {"subject1" , "subject2"};

var result = students_table
        .Where(s => s.Courses.Any(c => subject_names.Contains(c.Name)))
        .ToList();

Answer 2

试试这个：

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

namespace LinqAnswer
{
    public class Student
    {
        public int Age { get; set; }
        public string Name { get; set; }
        public List<Course> Courses { get; set; } = new List<Course>();

        public void AddCourse(Course course)
        {
            Courses.Add(course);
        }
    }

    public class Course
    {
        public int Id { get; set; }
        public string Name { get; set; }

        public List<Subject> Subjects { get; set; } = new List<Subject>();

        public void AddSubject(Subject subject)
        {
            Subjects.Add(subject);
        }
    }

    public class Subject
    {
        public string Name { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var students = new List<Student>
            {
                new Student { Age = 18, Name = "A" },
                new Student { Age = 19, Name = "B" },
                new Student { Age = 21, Name = "C" },
                new Student { Age = 22, Name = "D" },
                new Student { Age = 20, Name = "E" }
            };
            var courses = new List<Course>
            {
                new Course { Id = 1, Name = "C1" },
                new Course { Id = 2, Name = "C2" },
                new Course { Id = 3, Name = "C3" },
                new Course { Id = 4, Name = "C4" }
            };
            var subjects = new List<Subject>
            {
                new Subject { Name = "S1" },
                new Subject { Name = "S2" },
                new Subject { Name = "S3" }
            };
            students[0].AddCourse(courses[0]);
            students[0].AddCourse(courses[2]);
            students[1].AddCourse(courses[3]);
            students[2].AddCourse(courses[0]);
            students[2].AddCourse(courses[3]);
            students[3].AddCourse(courses[2]);
            students[4].AddCourse(courses[1]);

            courses[0].AddSubject(subjects[0]);
            courses[0].AddSubject(subjects[1]);
            courses[1].AddSubject(subjects[0]);
            courses[2].AddSubject(subjects[1]);
            courses[2].AddSubject(subjects[2]);
            courses[3].AddSubject(subjects[2]);

            var studentsWithSubjectS2 = from student in students
                                        from course in student.Courses
                                        where course.Subjects.IndexOf(subjects[2]) >= 0
                                        select student;
            foreach(var studentWithSubjectS2 in studentsWithSubjectS2)
            {
                Console.WriteLine($"{studentWithSubjectS2.Name}, Age={studentWithSubjectS2.Age}");
            }
        }
    }
}

Answer 3

假设EntityFramework并给Student一个StudentId属性，这是我的$ .02试试：

IList<int> studentIds = (from student in _context.Students
            from cource in
                student.Courses.Where(cource => _context.Subjects.Select(p => p.Name).ToList().Contains(cource.Name))
            select student.StudentId).ToList();

IQueryable<Student> selected = _context.Students.Where(p => studentIds.Distinct().Contains(p.StudentId));

多列表与单列表Linq查询比较

3 个答案: