Hi Valentin,
Your domain model is bugging you.
Your Product entity associates to the Cart entity 1-8 Where one product refers to a single cart and a Cart can be referenced by multiple Products. This last part bugs you in your page. Since multiple Products cab refer a Cart, you can not show the Product/Name, as this would be multiple.
Secondly, your Product can be ordered once, since it can only refer a single Cart.
Third, you have an enum “AddedToCart” in your product. Which isn’t a characteristic of the Product, but of the relation of the Product to a Cart. Since it will be added to a Cart multiple times. As you have modeled you can only add it to a Cart ones.
So you need the following domain model.
Adding to cart can be done by