Basket items need to be immutable, a snapshot of the product at that point in time…
Alex Mcauley

Yes of course! Also with product prices, you want to know what the customer paid, not what the price of the product is now. So you should have something like a BasketItem entity in this scenario as well. But I didn’t want to complicate the example needlessly as I didn’t think it was really relevant to the point I was trying to make.