NHibernate映射 - 一对一(或一对零)

public class UserMap : ClassMap<User>
{
    public UserMap()
    {
        Id(x => x.Id);
        Map(x => x.Name);
        HasOne(x => x.Address).Cascade.All();
    }
}

public class AddressMap : ClassMap<Address>
{
    public AddressMap()
    {
        Id(x => x.Id);
        Map(x => x.Street);
        Map(x => x.City);
        Map(x => x.ZipCode);
        References(x => x.User).Not.Nullable();
    }
}