You're missing an entity. You have an entity for the product, but not for each item. You can have the product "Mischau Grobe Mettwurst Pommersche Art" but you need to store the batches you get. You need an Inventory entity with relationship with the product, where you know how many items of that product you have, and when they expire. And you can have multiple batches of the same product with different expiration dates.