How to add multiple backend queries on a page

there is one page in my app where the data is coming from the backend in the row and that row contains the backend query for calling the data from the database like take an example (page showing services information like image, description and price and this all coming from the backend by implementing the backend query for query collection of services collection this collection also contains the id of the sub_category from which the service belongs) now there is on add button by which Document of service gets added into cart and sub_categoryCart Collections now sub_categoryCart collection also contains sub_catergory id, now i want apply the condititon that when customer clicks add button then before adding the service into the cart it should check that anu document with the sub_category id of that service already exists in sub_categoryCart collection or not, if exist then just update the quantity and price field of that document or else create the new document. so when I'm trying to add this condition I'm not getting the sub_categoryCart collection to check the sub_category id from because the sub_categoryCart collection is not added as a backend on that page, so tell where to add the sub_categoryCart collection as the backend query to check the document, is it even possible or not with this approach, if not then give me another approach