[{"Id":"12345-7","Stock":[{"Code":"1","Qty":5.0},{"Code":"3","Qty":7.0}]},{"Id":"22222-0","Stock":[{"Code":"3","Qty":10.0},{"Code":"10","Qty":2.0}]}]

db.collection.aggregate([{"$set":{"Code":["1","10"]}},{"$unwind":{"path":"$Code"}},{"$set":{"Availability":{"$cond":[{"$eq":[{"$filter":{"input":"$Stock","cond":{"$and":[{"$gte":["$$this.Qty",3]},{"$eq":["$$this.Code","$Code"]}]}}},[]]},"out of stock","in stock"]}}},{"$project":{"_id":0,"Id":1,"Code":1,"Availability":1}}])