New Post: Getting Item ID Before Document Saved.

I'm storing the Order ID in the Products (ordered) list. It's a simple parent-child relationship.

Good point about the various routes to the NewForm. I'll stick to doing it on the form.

I meant I didn't create the new item using SPS (to get the ID). I just put a redirect in .ready on the newform to a random editform. So I click "new" and end up in the edit form as suggested.