Question

我有一个看起来像这样的文件：

{
    "_id" : ObjectId("527a6b7c24a8874c078b9d10"),
    "day" : 6,
    "hour" : 15,
    "hourlyLocations" : [
        {
            "countryName" : "Spain",
            "countryCode" : "ES",
            "cityName" : "Madrid",
            "latitude" : 40,
            "longitude" : -4
        },
        {
            "countryName" : "United Kingdom",
            "countryCode" : "GB",
            "cityName" : "Soest",
            "latitude" : 51.5,
            "longitude" : -0.13
        }
    ],
    "minute" : 18,
    "month" : 11,
    "year" : 2013
}

“hourlyLocations”是一系列嵌入式文档（为简洁起见，这里只显示了两个）。

我正在尝试运行一个聚合，它将返回每个国家/地区，该国家/地区的所有城市（一次）以及每个城市的实例数量。

这是我到目前为止所得到的：

db.hourly.aggregate(
[
    { "$project" : { "hourly" : "$hourlyLocations" } },
    { "$unwind" : "$hourly" },
    { "$group" : { "_id" : { "country" : "$hourly.countryName" }, "city" : { "$push" : "$hourly.cityName" } } },
]
)

返回类似于：

的内容

{
        "_id" : {
            "country" : "Italy"
        },
        "city" : [
            "Manzano",
            "Cologno Monzese",
            "Rome",
            "Manzano",
            "Cologno Monzese",
            "Venice",
            "Milan",
            "Rome",
            "Milan",
            "Manzano",
            "Cologno Monzese",
            "Venice",
            "Milan",
            "Rome",
            "Milan",
            "Manzano",
            "Cologno Monzese",
            "Venice",
            "Milan",
            "Rome",
            "Manzano",
            "Cologno Monzese",
            "Venice",
            "Milan",
            "Casalnuovo di Napoli",
            "Manzano",
            "Cologno Monzese",
            "Venice",
            "Milan",
            "Casalnuovo di Napoli",
            "Milan"
        ]
    }

所以我得到了按城市分组的所有城市的所有实例。我现在要做的是按每个城市的实例数量分组并计算。像这样：

{
        "_id" : {
            "country" : "Italy"
        },
        "city" : [
            "Casalnuovo di Napoli" : "12"
            "Cologno Monzese" : "10",
            "Manzano" : "9",
            "Milan" : "6",
            "Rome" : "3",
            "Venice" : "1"
        ]
    }

我尝试过一些事情，但未能做到正确。如何根据我的要求获得每个国家/地区的每个城市的数量？

非常感谢，

尼克。

Answer 1

尝试：

db.hourly.aggregate(
[
    { "$project" : { "hourly" : "$hourlyLocations" } },
    { "$unwind" : "$hourly" },
    { $group: { _id: { country: "$hourly.countryName", city: "$hourly.cityName" }, count: { $sum: 1 } } },
    { $sort: { count: -1 } },
    {  $group: { _id: "$_id.country", cities: { $push: { city: "$_id.city", count: "$count"  } }  } }
]
)

这不是所要求的结构。相反，你得到：

{
    "_id" : {
        "country" : "Italy"
    },
    "cities" : [
        { "city": "Cologno Monzese", "count": 12},
        { "city": "Milan", "count": 6},
        { "city": "Rome", "count": 3},
    ]
}

Mongodb聚合，组和计数实例

1 个答案: