This is a problem of unidirectional one-to-one mapping in NHibernate.

Student.cs

public class Student
{
    public int ID { get; set; }
    public int Roll { get; set; }
    public int RegNo { get; set; }
    public string Name { get; set; }

    public StudentDetail StudentDetail { get; set; }
}

StudentDetail.cs

public class StudentDetail
{
    public int ID { get; set; }

    public string Father { get; set; }
    public string Mother { get; set; }
}

How can I map these classes (how do the hbm mapping files look like) to the following two distinct cases of one-to-one relationships?

1st case:

2nd case: