db={order:[{"_id":"62cdbae0421b250009acc329","cartitems":"62cdbaaf74c9c80009f5a4b2",},{"_id":"62d27e192b254600099ae680","cartitems":"62d27d9d91568c0009866d23",}],cart:[{"_id":"62cdbaaf74c9c80009f5a4b2","cartItems":[{"productCode":["NCK-1"],"Price":"56",},{"productCode":["NCK-2"],"Price":"56",}],},{"_id":"62d27d9d91568c0009866d23","cartItems":[{"productCode":["NCK-3"],"Price":"56",},{"productCode":["NCK-1"],"Price":"56",}],},]}

db.order.aggregate([{$lookup:{from:"cart",localField:"cartitems",foreignField:"_id",as:"cartitems",},},{$unwind:"$cartitems"},{$unwind:"$cartitems.cartItems"},{$group:{_id:{$first:"$cartitems.cartItems.productCode"},count:{$sum:{$toInt:"$cartitems.cartItems.Price"}},},},])