NHibernate one-to-one: null id generated for AccountDetail - nhibernate

Question

I got an exception "null id generated for AccountDetail" when mapping one-to-one relationship by using many-to-one with unique constraint.
Here's my SQL tables:
Account(Id, Name)
AccountDetail(AccountId, Remark)
AccountId is both primary and foreign key.
Here's my Domain Model (Account and AccountDetail):
public class Account
{
public virtual int Id { get; set; }
public virtual string Name { get; set; }
public virtual AccountDetail Detail { get; set; }
public Account()
{
Detail = new AccountDetail
{
Account = this
};
}
}
public class AccountDetail
{
public virtual int AccountId { get; set; }
public virtual Account Account { get; set; }
public virtual string Remark { get; set; }
}
Mapping (NHibenrate 3.3 mapping by code):
class AccountMap : ClassMapping<Account>
{
public AccountMap()
{
Table(typeof(Account).Name);
Id(c => c.Id, m => m.Generator(Generators.Native));
Property(c => c.Name);
OneToOne(c => c.Detail, m =>
{
m.Constrained(true);
m.Cascade(Cascade.All);
m.PropertyReference(typeof(AccountDetail).GetPropertyOrFieldMatchingName("Account"));
});
}
}
class AccountDetailMap : ClassMapping<AccountDetail>
{
public AccountDetailMap()
{
Table(typeof(AccountDetail).Name);
Id(c => c.AccountId, m =>
{
m.Column("AccountId");
m.Generator(Generators.Foreign<AccountDetail>(x => x.Account));
});
Property(c => c.Remark);
ManyToOne(c => c.Account, m =>
{
m.Column("AccountId");
m.Unique(true);
});
}
}
BTW: Can I remove the AccountId property in AccountDetail? That is, only use the Account property. Using both AccountId and Account properties in AccountDetail class looks not so object-oriented.
Thanks!

Answer 1

I can't say what's actually wrong, but comparing with my working one-to-one relation, I would map it like this:
class AccountMap : ClassMapping<Account>
{
public AccountMap()
{
Table(typeof(Account).Name);
// creates a auto-counter column "id"
Id(c => c.Id, m => m.Generator(Generators.Native));
// doesn't require a column, one-to-one always means to couple primary keys.
OneToOne(c => c.Detail, m =>
{
// don't know if this has any effect
m.Constrained(true);
// cascade should be fine
m.Cascade(Cascade.All);
});
}
}
class AccountDetailMap : ClassMapping<AccountDetail>
{
public AccountDetailMap()
{
Id(c => c.AccountId, m =>
{
// creates an id column called "AccountId" with the value from
// the Account property.
m.Column("AccountId");
m.Generator(Generators.Foreign(x => x.Account));
});
// should be one-to-one because you don't use another foreign-key.
OneToOne(c => c.Account);
}
}