EF-code-first many-to-many related objects generates two different SQL tables (MVC3) - asp.net-mvc-3

Question

I have read this great Q&A and I tried to make something similar. My Model classes are:
public class Person
{
public int PersonId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public ICollection<Course> CoursesAttending { get; set; }
public Person()
{
this.CoursesAttending = new List<Course>();
}
}
public class Course
{
public int CourseId { get; set; }
public string Title { get; set; }
public ICollection<Person> Students { get; set; }
}
public class PersonCourse
{
[Key, Column(Order = 0)]
public int PersonID { get; set; }
[Key, Column(Order = 1)]
public int CourseID { get; set; }
public virtual Person Student { get; set; }
public virtual Course StudentCourse { get; set; }
public int Mark { get; set; }
public string Comment { get; set; }
}
public class SchoolContext : DbContext
{
public DbSet<Course> Courses { get; set; }
public DbSet<Person> People { get; set; }
public DbSet<PersonCourse> PersonCourseLinks { get; set; }
public SchoolContext()
: base("ManyToManyTest")
{
}
}
Now, I try to add a new person and add a new course to his courses list:
[HttpPost]
public ActionResult Create(Person person)
{
if (ModelState.IsValid)
{
Course studentCourse;
try
{
studentCourse = db.Courses.ToList<Course>().First();
}
catch
{
studentCourse = new Course() { Title = "HTML" };
}
person.CoursesAttending.Add(studentCourse);
db.People.Add(person);
db.SaveChanges();
return RedirectToAction("Index");
}
return View(person);
}
Everything goes well, but when I open my created database, I see there are 2 link tables for the Person and Course classes - PersonCourses(with fields: PersonID, CourseID, Mark, Comment) and PersonCourse1(with fields: PersonID, CourseID), and only PersonCourse1 has rows (actually one row). Why does it happen? Did I do something not correct? I expect to see only one link table - the PersonCourses table...

Answer 1

I expect to see only one link table - the PersonCourses table
Then you have to link PersonCourse entity with Person entity though CoursesAttending navigational property. Same thing has to be done to Course entity.
public class Person
{
public int PersonId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public ICollection<PersonCourse> CoursesAttending { get; set; }
public Person()
{
this.CoursesAttending = new List<PersonCourse>();
}
}
public class Course
{
public int CourseId { get; set; }
public string Title { get; set; }
public ICollection<PersonCourse> Students { get; set; }
}

Answer 2

Give foreign key associations to the foreign key properties in your gerund table:
public class PersonCourse
{
[Key, Column(Order = 0)]
public int PersonID { get; set; }
[Key, Column(Order = 1)]
public int CourseID { get; set; }
[ForeignKey("PersonID")]
public virtual Person Student { get; set; }
[ForeignKey("CourseID")]
public virtual Course StudentCourse { get; set; }
public int Mark { get; set; }
public string Comment { get; set; }
}

Answer 3

Just so you now why your code wasn't working as expected:
public class PersonCourse
{
[Key, Column(Order = 0)]
public int PersonID { get; set; }
[Key, Column(Order = 1)]
public int CourseID { get; set; }
public virtual Person Person { get; set; } // Follow built in conventions
public virtual Course Course { get; set; }
public int Mark { get; set; }
public string Comment { get; set; }
}
This now follows the built in Entity Framework convention of having
public int [ClassName][Id] or [Id] //Database Foreign Key column
and
public NavigationProperty [ClassName] // Navigation Property