I've taken over the code, so I'm not 100% sicher how it was set up.
It's set up to work with miniShop2
there is a products table `modx_ms2_products` and a categories table `ms2_product_categories`, and a many-to-many table `ms2_product_categories`.
The Product-Categories has 4 fields: `id`, `product_id`, `category_id`, `catindex`
I'm using MIGX (MIXdb) to manage the catindex in manager on a grid
When category_id is selected as a filter, I want to have the catindex numbers be easily updated.
here is the setup:
http://pastebin.com/Hj6Kd4jN