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

public class Course
{
    public int Id { get; set; }
    public string Title { get; set; }
    public ICollection<Student> Students { get; set; }
}

protected override void Seed(StudentsContext context)
{
    var students = new List<Student>
    {
        new Student { Id = 1, Name = "stu1" },
        new Student { Id = 2, Name = "stu2" },
        new Student { Id = 3, Name = "stu3" },
    };

    students.ForEach(s => context.Students.Add(s));
    context.SaveChanges();

    var courses = new List<Course>
    {
        new Course { Id = 1, Title = "course1",
            Students = new List<Student>() { students[0], students[1] } },
        new Course { Id = 2, Title = "course2",
            Students = new List<Student>() { students[0] } },
        new Course { Id = 3, Title = "course3" },
    };

    courses.ForEach(c => context.Courses.Add(c));
    context.SaveChanges();
}

// GET api/Course
public IEnumerable<Course> GetCourses()
{
    return db.Courses.AsEnumerable();
}

[{"Id":1,"Title":"course1","Students":null},
 {"Id":2,"Title":"course2","Students":null},
 {"Id":3,"Title":"course3","Students":null}]

public IEnumerable<Course> GetCourses()
{
    return db.Courses.Include(c => c.Students).AsEnumerable();
}

[{"Id":1,"Title":"course1","Students":[{"Id":2,"Name":"stu2"}]},
 {"Id":2,"Title":"course2","Students":[{"Id":1,"Name":"stu1"}]},
 {"Id":3,"Title":"Operating Systems","Students":[]}]

var courses = new List<Course>
{
    new Course { Id = 1, Title = "course1",
        Students = new List<Student>() {
            new Student { Id = 1, Name = "stu1" },
            new Student { Id = 2, Name = "stu2" }
        }
    },
    new Course { Id = 2, Title = "course2",
        Students = new List<Student>() {
            new Student { Id = 1, Name = "stu1" }
        }
    },
    new Course { Id = 3, Title = "course2" }
};

public IEnumerable<Course> GetCourses()
{
    return db.Courses.Include(c => c.Students).AsEnumerable();
}

// GET api/Course
public IEnumerable<Course> GetCourses()
{
    return db.Courses.ToList();
}

// GET api/Course
public IEnumerable<Course> GetCourses()
{
    return db.Courses.Include((p) => p.Students).ToList();
}