How do I map two relationships between the same two entities?

Question

Some advice on how to even properly describe these relationships would be a great start. Something accurately described is a problem looking for a solution. I have entities User and Login, where Login describes basically a login session for one user. So, User normally has many Login instances. This relationship is only described on the Login side with a required, single User navigation property, and there is an implied, but not declared, Login collection on the User side.

Then, for the other relationship, a User is created under authorization of a Login, so this relationship is described on the User side, with a Login navigation property, and there is an implied, but not User collection on the Login side.

I don't do much DB modelling outside of using the DB tools, and they always just get relationships right for me, but now, I have to map these relationships for code first, using fluent mapping. How do I described these two relationships, what are the principle and dependent sides, and what are the multiplicities here?

Does it mean that login can be related to one user but its authorization to another? What is the authorization in that case? How many users can be in authorization for the login? — Ladislav Mrnka, Apr 22 '12 at 12:47
A user has a record of under which login that user was created. In that respect, 1 login can have many users. When a user logs in, 1 login is created for that user, but as users log in often, 1 user can have many logins, but is this respect, each login only has 1 user. — ProfK, Apr 22 '12 at 13:21

score 0 · Accepted Answer · answered Apr 22 '12 at 15:03

Code First tries to link up the two sides of what are probably the same relationship. When you instead have two different unidirectional relationships, then you need to tell Code First this by explicitly telling Code First that the inverse navigation property does not exist using WithMany() with no arguments:

public class User
{
    public int Id { get; set; }
    public int LoginId { get; set; }
    public virtual Login Login { get; set; }
}

public class Login
{
    public int Id { get; set; }
    public int UserId { get; set; }
    public virtual User User { get; set; }
}

public class SomeContext : DbContext
{
    public DbSet<User> Users { get; set; }
    public DbSet<Login> Logins{ get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<User>()
            .HasRequired(e => e.Login)
            .WithMany()
            .HasForeignKey(e => e.LoginId);

        modelBuilder.Entity<Login>()
            .HasRequired(e => e.User)
            .WithMany()
            .HasForeignKey(e => e.UserId);
    }
}

Thanks, that looks more like what I'm looking for. – ProfK Apr 22 '12 at 16:02 — ProfK, Apr 22 '12 at 16:02

How do I map two relationships between the same two entities?

1 Answers1