Q:

EF 7 (Beta 7) One-to-One Relationship

I've noticed questions that have answered this problem for earlier beta versions of EF 7 (like here), but I haven't seen it solved for Beta 7, so here it goes:
I have 2 entities, simplified as follows:
public class FirstEntity
{
    public int FirstEntityID { get; set; }
    /*
        Other fields here
    */
    public int? SecondEntityID { get; set; }
    public SecondEntity SecondEntityProperty { get; set; }
}

public class SecondEntity
{
    public int FirstEntityID { get; set; } 
    /*
        Other fields here
    */
    public FirstEntity FirstEntityProperty { get; set; }
}

The way to map everything has changed so much from earlier versions. How do I map these two entities in a One-to-One relationship?

A:

It has been changed for EF7 rc1-final.
modelBuilder.Entity<FirstEntity>()
            .HasOne(q => q.SecondEntity)
            .WithMany()
            .HasForeignKey(q => q.SecondEntityID);

upd:
modelBuilder.Entity<FirstEntity>()
            .HasOne(q => q.SecondEntity)
            .WithOne(v => v.FirstEntity)
            .HasForeignKey<FirstEntity>(q => q.SecondEntityID);

