Ebay API - How to get an item's ancestor/root category?

Question

I'm retrieving the item info of many items using getMultipleItems in the Shopping API, and I need to find-out the items' root category. In the US site (0), the root categories are here: http://www.isoldwhat.com/getcats/fullcategorytree.php

How can I tell which of these an item belongs to (for example, "Computers/Tablets & Networking")? Can I do it within getMultipleItems (or getSingleItem) or do I need another call?

It seems like a short question, but this problem is shared with my use of the Amazon API to which I've been doing extensive research and I decided to resolve it on my eBay end. The "problem" is determining the selling fee, which can be done on Amazon's side, by getting the ProductGroup of the item, or by using eBay's root categories, and matching either one to the fee table Amazon defined for it's commission rates. In this case, there's not a lot of turn-out to refer to here to show I looked everything up.

The getCategoryInfo and related category-info-searching doesn't pertain to particular items. I get a <primarycategoryid> N/V pair in my item responses, but (I'm pretty sure) that's a leaf category (mapping 10,000+ leaf categories [even just the fraction I would use] to Amazon's product group-specific fee table would be a hell of a pain).

Again, how do I trace an <item> to it's ancestor/root category?

Answer 1

You can trace the root of a category via the PrimaryCategoryIDPath field that is returned when calling GetMultipleItems.

Keep in mind that this information is not returned unless you have specified Details in the IncludeSelector field as part of your request.

More information on PrimaryCategoryIDPath can be found here.