Here's what I'm trying to do...
A given item in our store might be in multiple numerical "Product Groups". We also need to use those product groups to qualify/disqualify those items for coupons and sales rules.
If I define "Product Group" as custom attribute through EAV, the best I can do is set the Backend Model to "array", and have the multiple product groups saved as comma-delimited text in a varchar field. This is obviously less than ideal (and doesn't even convert back to an array on load).
Is there any way to have true one-to-many database rows for a product's custom attributes?