如何在mongodb中使用$project显示数组中的特定字段

我有一个包含航班信息的数据库。我试图找到延迟时间最少的类别。我设法找到并显示了类别的最小分钟数，但没有显示类别本身

我试着在每个字段后面加上“：true”来显示它

db.delayData.aggregate([{
                $group: {
                    "_id": "$carrier",
                    "arr_sum": {
                        $sum: "$arr_delay"
                    },
                    "carrier_sum": {
                        $sum: "$carrier_delay"
                    },
                    "weather_sum": {
                        $sum: "$weather_delay"
                    },
                    "nas_sum": {
                        $sum: "$nas_delay"
                    },
                    "sec_sum": {
                        $sum: "$security_delay"
                    },
                    "late_air_sum": {
                        $sum: "$late_aircraft_delay"
                    }
                }
            },
            {
                $project {
                    "min_delay_category": {
                        $min["$arr_sum", "$carrier_sum", "$weather_sum", "$nas_sum", "$sec_sum", "$late_air_sum"]
                    }
                }
            ]).pretty()

我想要这样的东西： {id:“VX”，“最小延迟”类别：1449，“秒和”…}

我试着写：

     ..."$sec_sum":1,"$late_air_sum":1]

但错误信息是：

     "missing ] after element list"

当我写道：

      ...{"sec_sum":1},{"late_air_sum":1}] 

我没有错误消息，但它会给我至少第二个结果，而不是第一个。 例如：

      { "_id" : "VX", "min_delay_category" : 69081 }

---

但是“VX”的真实结果是1449，下面的查询可以得到预期的输出：

db.collection.aggregate([
    {
        $project:{
            "carrier":1,
            "category.arr_delay":"$arr_delay",
            "category.carrier_delay":"$carrier_delay",
            "category.weather_delay":"$weather_delay",
            "category.nas_delay":"$nas_delay",
            "category.security_delay":"$security_delay",
            "category.late_aircraft_delay":"$late_aircraft_delay"
        }
    },
    {
        $project:{
            "carrier":1,
            "categories":{
                $objectToArray:"$category"
            }
        }
    },
    {
        $unwind:"$categories"
    },
    {
        $group:{
            "_id":{
                "carrier":"$carrier",
                "category":"$categories.k"
            },
            "carrier":{
                $first:"$carrier"
            },
            "category":{
                $first:"$categories.k"
            },
            "total_delay":{
                $sum:"$categories.v"
            }
        }
    },
    {
        $sort:{
            "total_delay":1
        }
    },
    {
        $group:{
            "_id": "$carrier",
            "carrier":{
                $first:"$carrier"
            },
            "category":{
                $first:"$category"
            },
            "minimum_delay":{
                $first:"$total_delay"
            }
        }
    },
    {
        $project:{
            "_id":0
        }
    }
]).pretty();

数据集：

{
    "_id" : ObjectId("5d5b5058435c7584459b7bae"),
    "year" : 2003,
    "month" : 6,
    "carrier" : "AA",
    "carrier_name" : "American Airlines Inc.",
    "airport" : "ABQ",
    "airport_name" : "Albuquerque, NM: Albuquerque International Sunport",
    "arr_flights" : 307,
    "arr_del15" : 56,
    "carrier_ct" : 14.68,
    "weather_ct" : 10.79,
    "nas_ct" : 19.09,
    "security_ct" : 1.48,
    "late_aircraft_ct" : 9.96,
    "arr_cancelled" : 1,
    "arr_diverted" : 1,
    "arr_delay" : 2530,
    "carrier_delay" : 510,
    "weather_delay" : 621,
    "nas_delay" : 676,
    "security_delay" : 25,
    "late_aircraft_delay" : 698,
    "" : ""
},
{
    "_id" : ObjectId("5d5b5058435c7584459b7bbe"),
    "year" : 2003,
    "month" : 6,
    "carrier" : "AA",
    "carrier_name" : "American Airlines Inc.",
    "airport" : "ABQ",
    "airport_name" : "Albuquerque, NM: Albuquerque International Sunport",
    "arr_flights" : 307,
    "arr_del15" : 56,
    "carrier_ct" : 14.68,
    "weather_ct" : 10.79,
    "nas_ct" : 19.09,
    "security_ct" : 1.48,
    "late_aircraft_ct" : 9.96,
    "arr_cancelled" : 1,
    "arr_diverted" : 1,
    "arr_delay" : 2530,
    "carrier_delay" : 510,
    "weather_delay" : 621,
    "nas_delay" : 676,
    "security_delay" : 2512,
    "late_aircraft_delay" : 698,
    "" : ""
}

{ "carrier" : "AA", "category" : "carrier_delay", "minimum_delay" : 1020 }

输出：

{
    "_id" : ObjectId("5d5b5058435c7584459b7bae"),
    "year" : 2003,
    "month" : 6,
    "carrier" : "AA",
    "carrier_name" : "American Airlines Inc.",
    "airport" : "ABQ",
    "airport_name" : "Albuquerque, NM: Albuquerque International Sunport",
    "arr_flights" : 307,
    "arr_del15" : 56,
    "carrier_ct" : 14.68,
    "weather_ct" : 10.79,
    "nas_ct" : 19.09,
    "security_ct" : 1.48,
    "late_aircraft_ct" : 9.96,
    "arr_cancelled" : 1,
    "arr_diverted" : 1,
    "arr_delay" : 2530,
    "carrier_delay" : 510,
    "weather_delay" : 621,
    "nas_delay" : 676,
    "security_delay" : 25,
    "late_aircraft_delay" : 698,
    "" : ""
},
{
    "_id" : ObjectId("5d5b5058435c7584459b7bbe"),
    "year" : 2003,
    "month" : 6,
    "carrier" : "AA",
    "carrier_name" : "American Airlines Inc.",
    "airport" : "ABQ",
    "airport_name" : "Albuquerque, NM: Albuquerque International Sunport",
    "arr_flights" : 307,
    "arr_del15" : 56,
    "carrier_ct" : 14.68,
    "weather_ct" : 10.79,
    "nas_ct" : 19.09,
    "security_ct" : 1.48,
    "late_aircraft_ct" : 9.96,
    "arr_cancelled" : 1,
    "arr_diverted" : 1,
    "arr_delay" : 2530,
    "carrier_delay" : 510,
    "weather_delay" : 621,
    "nas_delay" : 676,
    "security_delay" : 2512,
    "late_aircraft_delay" : 698,
    "" : ""
}

{ "carrier" : "AA", "category" : "carrier_delay", "minimum_delay" : 1020 }

聚合阶段详细信息：

{
    "_id" : ObjectId("5d5b5058435c7584459b7bae"),
    "year" : 2003,
    "month" : 6,
    "carrier" : "AA",
    "carrier_name" : "American Airlines Inc.",
    "airport" : "ABQ",
    "airport_name" : "Albuquerque, NM: Albuquerque International Sunport",
    "arr_flights" : 307,
    "arr_del15" : 56,
    "carrier_ct" : 14.68,
    "weather_ct" : 10.79,
    "nas_ct" : 19.09,
    "security_ct" : 1.48,
    "late_aircraft_ct" : 9.96,
    "arr_cancelled" : 1,
    "arr_diverted" : 1,
    "arr_delay" : 2530,
    "carrier_delay" : 510,
    "weather_delay" : 621,
    "nas_delay" : 676,
    "security_delay" : 25,
    "late_aircraft_delay" : 698,
    "" : ""
},
{
    "_id" : ObjectId("5d5b5058435c7584459b7bbe"),
    "year" : 2003,
    "month" : 6,
    "carrier" : "AA",
    "carrier_name" : "American Airlines Inc.",
    "airport" : "ABQ",
    "airport_name" : "Albuquerque, NM: Albuquerque International Sunport",
    "arr_flights" : 307,
    "arr_del15" : 56,
    "carrier_ct" : 14.68,
    "weather_ct" : 10.79,
    "nas_ct" : 19.09,
    "security_ct" : 1.48,
    "late_aircraft_ct" : 9.96,
    "arr_cancelled" : 1,
    "arr_diverted" : 1,
    "arr_delay" : 2530,
    "carrier_delay" : 510,
    "weather_delay" : 621,
    "nas_delay" : 676,
    "security_delay" : 2512,
    "late_aircraft_delay" : 698,
    "" : ""
}

{ "carrier" : "AA", "category" : "carrier_delay", "minimum_delay" : 1020 }

• 第一阶段：将所有延迟作为

  类别的一部分进行预测

• 第二阶段：将

  类别

  转换为键值对数组 其中，“k”是延迟类型，“v”是延迟类型
• 第三阶段：展开准备好的阵列
• 第四阶段：根据

  承运人和
  延迟类型（k）
  进行分组，并对每种类型的延迟进行汇总

• 第五阶段：按升序对计算的总延迟进行排序
• 第六阶段：在

  载体上分组并获取第一份文档
  哪个保持最小的延迟

---

欢迎来到StackOverflow。预期的产出不清楚。请您发布示例数据和适当的预期输出。延迟的类别有：承运人延迟-承运人造成的总延迟分钟数。天气延误-由于天气原因造成的延误总分钟数，还有4分钟：飞机抵达延误、nas延误、安全延误、飞机延误。id表示航空公司代码（承运人）。对于每一家航空公司，我都有很多航班。我需要计算每个类别的延误总数，以确定每个航空公司哪一类别的延误时间最少。预期的输出是：{“\u id”：“VX”，类别：security\u delay，“min\u delay\u category”：1449}或：{“\u id”：“VX”，“min\u delay\u category”：security\u delay}。好的。如果你能发布一份样本文档，这将有助于准备一个完美的查询。{“_id”：ObjectId（“5d5b5058435c7584459b7bae”），“年”：2003，“月”：6，“承运人”：“AA”，“承运人名称”：“美国航空公司”，“机场”：“ABQ”，“机场名称”：“阿尔伯克基，新墨西哥州：阿尔伯克基国际太阳港”，“arr_航班”：307，“arr_del15”：56，“航母起飞时间”：14.68，“天气起飞时间”：10.79，“航母起飞时间”：19.09，“安全起飞时间”：1.48，“飞机晚点起飞时间”：9.96，“飞机晚点起飞取消”：1，“飞机晚点起飞时间”：1，“飞机晚点起飞时间”：2530，“航母晚点起飞时间”：510，“天气晚点起飞时间”：621，“飞机晚点起飞时间”：676，“安全晚点起飞时间”：25，“飞机晚点起飞时间”：698“：”）