Relationship Doubt

Consider user cart document with relationship with one-to-many products. Obviously Each product should also contain counts based on user choices. My question is how can we integrate count into specific products. Note:- Product should not be updated. Only Cart Document should be updated.

One solution that came to my mind is storing count as array of string {id: productId: count:2}. i.e.

Is there any other better way? With/without relationship?

I would probably have a cart Collection. Each item in the cart would be a Document, with a reference to the user and a Relationship with a single product, then a qty Attribute

This will require many documents for single user cart. That's why I am tried to keep all products in on doc

Well, if you want only one Document for the cart, the only option I see is to have an Array Attribute with the product IDs and quantites (as you suggested). You could also have another Attribute with a many-to-many Relationship with all the products, to avoid having to make a second request out to get the products each time.

Although I don't see any inherent issue with having many Documents for each cart