Im using exactly that in my combos but as the fill method I use a custom one instead of one that came with the framework because I have a compound index and as I see the methods don´t take care of the business rules (i've put the relationship with the parent on the child BO) nor the PK's on the tables (or may be yes but I don't know how).

So, can I use fillby... or another standard method if I had to pass a compound index?