Is it hard to allow this?

Well, it won't be so trivial and it also looks quite suspicious to me to have maps whose elements are updated, but indices aren't...

Maybe a more "explicit" design would be better? Some object that has a method CountryCode GetCountryCode(string code) and whose implementation uses an NHibernate query.

the "explicit" way is what we are taking now. I am just thinking, in doing this way, we cannot just make use of what Hashtable already provided.

Anyways, it's just my personal feeling, I can understand why Hibernate is doing this way, just in this way, <map> is really seldom used, as I discribed in my previous post: Usually, I put "id" as the index, and when I remove a child from a one-to-many <map>, I don't expect the child object's id be removed.

But, if it is not a trivial change, I am not pushing it.

Thanks anyways.