Check if items are already in cart


I’m trying to limit the quantity of a product a customer can buy. I could limit the quantity that can be added to the cart with Custom attributes. The problem is that if the costumer clicks on add to cart again, it will add the product again.

So I need to add a check on the button, so every time when clicked to check if that product is already in the cart. Is it possible?

Any hints are highly appreciated!

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