Saving 2 dependent models in one form (one needs other's ID)

I’ve got a problem with saving 2 dependent models in one form (one needs other’s id).
Can anybody help?

Details: http://railsforum.com/viewtopic.php?id=17859

Don't call your model transaction. An association called transaction will override a built in rails method which is used when saving a record.

Fred

maybe use a dummy interemediate value then 'really' save them [?]