NAV 2013 R2. TableRelation to a compound key.

Hi!

I'm trying to create a new field "product subgroup" in the Item table.

So in NAV we have Item Categories, and then we have Product groups, that are related with Item category code. The main key of Product groups is "Item Category Code,Code"

Now I create a new table called "subgroup", and I create the field "product group code".

The problem is that I can create the tablerelation to the product group's "code" field, but not to the key "Item Category Code,Code"

Does this mean I also have to create the "Item category" field in my "subgroup" table? or is there any workaround?

The idea is that when I take an item and fill in the Item Category and the Product Group, I only want to get the subgroups that belong to the selected Item category and product group.