Prevent duplicate records on join-table per parent Record
I have a products layout with a portal to a join table where a user can assign inks to the product. I want to prevent a user from assigning the same ink to a product multiple times. The inks can be used with many products.
Products Table > Inks Selected Table < Inks Table
How do you resolve this? I searched around and perhaps I'm phrasing it wrong but I could not find an answer.