using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

         var subjects = new List<Subject>

            {

                new Subject { SubjectID =1, Name = "Mathematics" },

                new Subject { SubjectID =2, Name = "History" },

                new Subject { SubjectID =3, Name = "Science" }

            };

​

            var subjectStudents = new List<SubjectStudent>

            {

                new SubjectStudent { SubjectStudentID =1, SubjectID = 2, StudentID = 1000 },

                new SubjectStudent { SubjectStudentID =2, SubjectID = 1, StudentID = 1001 },

                new SubjectStudent { SubjectStudentID =3, SubjectID = 3, StudentID = 1003 },

                new SubjectStudent { SubjectStudentID =4, SubjectID = 1, StudentID = 1005 }

            };

​

            var studentsGrade = new List<StudentGrade>

            {

                new StudentGrade { StudentGradeID =1, StudentID = 1001, GradeID = 1 },

                new StudentGrade { StudentGradeID =2, StudentID = 1003, GradeID = 2 },

                new StudentGrade { StudentGradeID =3, StudentID = 1005, GradeID = 3 }

            };

​

            var result = (from s in subjects

                          join ss in subjectStudents on s.SubjectID equals ss.SubjectID into SubjectStudents

                          select new

                          {

                              SubjectID = s.SubjectID,

                              Students = from ss in SubjectStudents

                                         join g in studentsGrade on ss.StudentID equals g.StudentID 

                                         select new { StudentId = ss.StudentID, GradeId = g.GradeID }

                           })

                .ToList();

​

            foreach (var subject in result)

            {

                Console.WriteLine("Subject: {0}",subject.SubjectID);

                foreach (var student in subject.Students)

                {

                    Console.WriteLine("Student: {0}",student.StudentId);

                    Console.WriteLine("\tGrade: {0}", student.GradeId);

                }

                Console.WriteLine();

            }

    }

}

​

public class Subject

    {

        public int SubjectID { get; set; }

        public string Name { get; set; }

    }

​

    public class SubjectStudent

    {

        public int SubjectStudentID { get; set; }

        public int SubjectID { get; set; }

        public int StudentID { get; set; }

    }

​

    public class StudentGrade

    {

        public int StudentGradeID { get; set; }

        public int StudentID { get; set; }

        public int GradeID { get; set; }

    }