db={"products":[{"_id":"61c53eb76eb2dc65de621bd0","name":"Product 1","price":80},{"_id":"61c53efca0a306c3f1160754","name":"Product 2","price":10}],"orders":[{"_id":"61c53fb7dca0579de038cea8","products":[{"_id":"61c53eb76eb2dc65de621bd0","quantity":1},{"_id":"61c53efca0a306c3f1160754","quantity":2},]}]}

db.orders.aggregate([{$match:{_id:"61c53fb7dca0579de038cea8"}},{$lookup:{from:"products",localField:"products._id",foreignField:"_id",as:"productDetail"}},{$project:{products:{$map:{input:"$products",as:"product",in:{$mergeObjects:["$$product",{$first:{$filter:{input:"$productDetail",cond:{$eq:["$$this._id","$$product._id"]}}}}]}}}}}])