[{"productID":1,"reviews":[{"_id":1,"likes":[{"userID":1},{"userID":2}],"dislikes":[{"userID":3},{"userID":4}],"comment":"first comment"},{"_id":2,"likes":[{"userID":1},{"userID":2}],"dislikes":[{"userID":3},{"userID":4}],"comment":"second comment"}]}]

db.collection.aggregate([{$match:{productID:1}},{$unwind:"$reviews"},{$match:{"reviews._id":2}}])