Comment 5 for bug 146165

I would be very happy if you get it going; it will probably speed it
up, make it more readable, and also let it work with foreign branches.
 The add code at the moment does a lot of manipulations on the
inventory after reading it in, which makes it easy to keep track of
things like adding parents before children, but it does also mean it's
very tied to having mutable inventories.

Perhaps we can pair on this at the sprint if you don't solve it beforehand.

Martin