I had to add a parent ID column to the hierarchy table and backfill for all the previously created posts.

I was already in there to make the performance mod I mentioned in the Open Forum, so I did it all at once.

Ironically enough. Set-trees can easily give you ALL ancestors, but not just the immediate parent. However, forum software is (usually) only concerned with the entire tree.

So, I added a parent ID field that gets prefilled at post creation time. It's never used for navigation or tree display though, just that link. :-P