Let me preface this question with saying that I am very new to Orchard development. :-)
I am in the process of creating an eCommerce module for Orchard that, 1) on the front-end displays images of products and 2) on the back-end (admin) allows one to enter products and data (prices, quantity on hand, etc), customers, orders, etc).
For the products, I've already created ProductCategory contentpart (Name, CreatedOn, and Active). I'd like to create a ProductSubCategory contentpart that would be linked to ProductCategory (like a foreign key in a database).
How might one do that?