Mongoose聚合改进

Question

鉴于此数据集和此mongodb，如何正确地将此聚合转换为Mongoose？

我已经包含了使用mongoose的代码，但是我想知道这是否是正确的方法，如果可以改进这种聚合？

感谢。

db.cars.aggregate(
    //De-normalized the nested array of accounts
    {"$unwind": "$accounts"},
    //De-normalized the nested array of cars
    {"$unwind": "$accounts.cars"},
    //match carId to 3C
    {"$match": {"accounts.cars.carId" : "3C"}},
    //Project the accounts.cars object only
    {"$project" : {"accounts.cars" : 1}}
).pretty();

我正在努力改进的Mongoose版本：

Car.aggregate()
  .unwind('accounts')
  .unwind('accounts.cars')
  .match({'accounts.cars.carId' : "3C"})
  .project({"accounts.cars": 1, _id: 0})
  .exec(function (err, carsObj) {});

和数据集（汽车）：

{ 
        "_id" : ObjectId("56223329b64f07a40ef1c15c"), 
        "username" : "john", 
        "email" : "john@john.com", 
        "accounts" : [
            {
                "_id" : ObjectId("56322329b61f07a40ef1c15d"), 
                "cars" : [
                    {
                        "carId" : "6A", 
                        "_id" : ObjectId("56323329b64f07a40ef1c15e")
                    },
                    {
                        "carId" : "6B", 
                        "_id" : ObjectId("56323329b64f07a40ef1c15e")
                    }
                ]
            }
        ]
    },
    { 
        "_id" : ObjectId("56223125b64f07a40ef1c15c"), 
        "username" : "paul", 
        "email" : "paul@paul.com", 
        "accounts" : [
            {
                "_id" : ObjectId("5154729b61f07a40ef1c15d"), 
                "cars" : [
                    {
                        "carId" : "5B", 
                        "_id" : ObjectId("56323329854f07a40ef1c15e")
                    }
                ]
            },
            {
                "_id" : ObjectId("56322117b61f07a40ef1c15d"), 
                "cars" : [
                    {
                        "carId" : "6G", 
                        "_id" : ObjectId("51212929b64f07a40ef1c15e")
                    },
                    {
                        "carId" : "3C", 
                        "_id" : ObjectId("51273329b64f07a40ef1c15e")
                    },
                    {
                        "carId" : "4N", 
                        "_id" : ObjectId("51241279b64f07a40ef1c15e")
                    }
                ]
            }
        ]
    }

聚合返回的内容是：

[
  { accounts:
     { cars:
        {
          "carId" : "3C", 
          "_id" : ObjectId("51273329b64f07a40ef1c15e")
        }
     }
  }
]