Circular relation one to many

Question

I am having an issue with my database model. I am fairly new to this, thus sorry in advance. Here are how my auto generated classes look like...

Session Model

public partial class Session
{
    public Session()
    {
        this.Tutors = new HashSet<Tutor>();
    }

    public int SessionId { get; set; }
    public int StudentStudentId { get; set; }

    public virtual Student Student { get; set; }
    public virtual ICollection<Tutor> Tutors { get; set; }
}

Student Model

public partial class Student
{
    public Student()
    {
        this.Sessions = new HashSet<Session>();
    }

    public int StudentId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public virtual ICollection<Session> Sessions { get; set; }
}

Controller

    public Student Get(int id)
    {

        using(var db = new studytree_dbEntities())
        {

            Student s = db.Students.FirstOrDefault(i => i.StudentId == id);



         return s;
        }
    }

I know what the problem is. The database queries from the student table receiving the data. Since it has a sessionid column, it goes to the session table and queries the session. But since it is a one to many relationship, the session table has one student, thus a loop is created. A student grabs it session and the session grabs its student etc.... How can I make it so that it only goes one level deep. What I want to be able to do is query a student and get all its properties.

By "all its properties" does that include the student's sessions? — Jeremy Cook, Apr 23 '14 at 14:36

Jeremy Cook · Accepted Answer · 2014-04-23T15:51:22.087

0

One approach is to manually materialize the student and her sessions, without materializing the session's student reference. This code assumes that Tutor does not reference any students. If it does you'll need to manually materialize Tutor as well.

using(var db = new studytree_dbEntities())
{

    Student s = db.Students
        .Where(s => s.StudentId == id)
        .ToList()
        .Select(s => new Student {
            FirstName = s.FirstName,
            LastName = s.LastName,
            Sessions = s.Sessions.Select(session => new Session {
                Tutors = session.Tutors
            }),
        })
        .FirstOrDefault();
    return s;
}

edited Apr 23 '14 at 15:51

answered Apr 23 '14 at 14:40

Jeremy Cook

20,840
9
71
77

I get this error. An exception of type 'System.NotSupportedException' occurred in System.Data.Entity.dll but was not handled in user code Additional information: The entity or complex type 'studytree_dbModel.Student' cannot be constructed in a LINQ to Entities query. – user3516446 Apr 23 '14 at 15:19
I apologize. I've updated my answer and use `ToList` to get an in memory copy of the student. Try the change out. – Jeremy Cook Apr 23 '14 at 15:54

Circular relation one to many

1 Answers1