db={"stockIn":[{serial:"stk0001",date:"2021-06-11",productInTransation:[{_id:"60ae220b066b8d9861118cb1",productId:"60ae220b066b8d9861118cb5",qty:2},{_id:"60ae220b066b8d9861118cb1",productId:"60ae220b066b8d9861118cb4",qty:2}]}],"products":[{_id:"60ae220b066b8d9861118cb5",name:"sepatu"},{_id:"60ae220b066b8d9861118cb4",name:"sendal"}]}

db.stockIn.aggregate([{$unwind:"$productInTransation"},{"$lookup":{"from":"products","localField":"productInTransation.productId","foreignField":"_id","as":"productInTransation.product"}},{"$addFields":{"productInTransation.product":{"$ifNull":[{"$arrayElemAt":["$productInTransation.product",0]},[]]}}},{"$group":{"_id":"$_id","date":{"$first":"$date"},"serial":{"$first":"$serial"},"productInTransation":{$push:"$productInTransation"}}}])