public class Role
{
public virtual int Id { get; set; }
public virtual string Name { get; set; }

public virtual int Level { get; set; }

public virtual bool Isman { get; set; }

public virtual User User { get; set; }

 }

}

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

public virtual string Username { get; set; }

public virtual string Password { get; set; }

public virtual int Age { get; set; }

public virtual string Email { get; set; }

}
}

子表是role，父表是user

 roletemp.User = peer.LoginUser;

public void SaveRole(Role role) {
using (var session = NhibernateHelper.OpenSession())
{
using (var transaction = session.BeginTransaction())
{

session.Save(role);
transaction.Commit();

}

}

}

执行出错 object references an unsaved transient instance before flushing

要怎么改能保存role？