db={"inventories":[{"id":0,"count":10,"productId":0},{"id":1,"count":0,"productId":1},{"id":2,"count":4,"productId":0},{"id":3,"count":0,"productId":1}],"products":[{"id":0,"title":"test","inventories":[0,2]},{"id":1,"title":"test 1","inventories":[1,3]}]}

db.products.aggregate([{"$lookup":{"from":"inventories","localField":"inventories","foreignField":"productId","pipeline":[{"$group":{"_id":null,"sum":{"$sum":"$count"}}}],"as":"inventorySum"}},{"$match":{"inventorySum.sum":{"$gt":0}}},{"$unset":["_id","inventorySum"]}])