Question

I’m using the Entity Framework 4 code first approach to design my database in ASP MVC 3 and I ran into a bit of a hitch. I have a POCO class as below:

public class User
{
    [Key]
    public Guid UserID { get; set; }
    public string UserName { get; set; }
    public DateTime CreationDate { get; set; }
    public string Email { get; set; }
    public int Points { get; set; }
    public Session ActiveSession { get; set; }
    public ICollection<Session> InSessions { get; set; }
}

with Session as another one of my model classes defined elsewhere, with ICollection<User> as one of its properties. If I remove the public Session ActiveSession { get; set; } property from the User class, then the many-to-many mapping and UserSessions intermediate table are constructed correctly, but when I add the ActiveSession one-to-one mapping back in, it breaks the many-to-many mapping and the intermediate table is not constructed. Instead the Users table has a single foreign key to the Sessions table each for both the ActiveSession and InSessions properties. Any ideas why this is happening?

Answer 1

In your case EF thinks that ICollection<User> in Session class is the Many end of the one to many relationship created by ActiveSession.

So you need to configure mannualy

modelBuilder.Entity<User>().HasOptional(u => u.ActiveSession)
   .WithMany()
   .Map(u => u.MapKey("ForeignKeyColumn"));

modelBuilder.Entity<User>()
   .HasMany(u => u.InSessions)
   .WithMany(s => s.Users)
   .Map(m =>
       {
           m.ToTable("UserSessions");
           m.MapLeftKey("UserID");
           m.MapRightKey("SessionID");
       });