mongodb - MongoDB，通过另一个键值将内部哈希键值分组

我的收藏中有以下四个元素：

/* 1 */
{
  "demographics": [
    {
      "key": "country",
      "value": "ES"
    },
    {
      "key": "city",
      "value": "Sevilla"
    },
    {
      "key": "region",
      "value": "Andalucía"
    }
  ]
}

/* 2 */
{
  "demographics": [
    {
      "key": "city",
      "value": "Cádiz"
    },
    {
      "key": "country",
      "value": "ES"
    },
    {
      "key": "region",
      "value": "Andalucía"
    }
  ]
}

/* 3 */
{
  "demographics": [
    {
      "key": "country",
      "value": "GB"
    },
    {
      "key": "region",
      "value": "Greater London"
    },
    {
      "key": "city",
      "value": "London"
    }
  ]
}

/* 4 */
{
  "demographics": [
    {
      "key": "country",
      "value": "ES"
    },
    {
      "key": "region",
      "value": "Andalucía"
    },
    {
      "key": "city",
      "value": "Sevilla"
    }
  ]
}

我想按以下方式对它们进行分组：
demographic.value当demographic.key = "country"时
demographic.value当demographic.key = "region"时
demographic.value当demographic.key = "city"时
结果是这样的：

{ "values": ["ES", "Andalucía", "Sevilla"], "count": 2 }
{ "values": ["ES", "Andalucía", "Cádiz"], "count": 1 }
{ "values": ["GB", "Greater London", "London"], "count": 1 }

注意：注意demographics数组元素的顺序可能并不总是相同的。
我试过了

db.getCollection('test').aggregate(
  [
    { "$unwind": "$demographics" },
    {
      "$project" :{
        "_id": 0,
        "demographics.key": 1,
        "demographics.value": 1
      }
    },
    {
      "$group" : {
        "_id": {
          "key": "$demographics.key",
          "value": "$demographics.value"
        },
        "count": { "$sum": 1 }
      }
    },
    {
      "$group" : {
        "_id": "$_id.key",
        "values": { "$push": { "value": "$_id.value", "count": "$count" } }
      }
    }
  ]
)

这给了我一个结果：

/* 1 */
{
  "_id": "country",
  "values": [
    {
      "value": "GB",
      "count": 1.0
    },
    {
      "value": "ES",
      "count": 3.0
    }
  ]
}

/* 2 */
{
  "_id": "region",
  "values": [
    {
      "value": "Greater London",
      "count": 1.0
    },
    {
      "value": "Andalucía",
      "count": 3.0
    }
  ]
}

/* 3 */
{
  "_id": "city",
  "values": [
    {
      "value": "London",
      "count": 1.0
    },
    {
      "value": "Cádiz",
      "count": 1.0
    },
    {
      "value": "Sevilla",
      "count": 2.0
    }
  ]
}

但这不是我要找的人

最佳答案

您可以尝试运行以下管道：

db.test.aggregate([
    { "$unwind": "$demographics" },
    { "$sort": { "demographics.key": 1, "demographics.value": 1 } },
    {
        "$group": {
            "_id": "$_id",
            "values": { "$push": "$demographics.value" }
        }
    },
    {
        "$group": {
            "_id": "$values",
            "count": { "$sum": 1 }
        }
    },
    {
        "$project": {
            "_id": 0, "values": "$_id", "count": 1
        }
    }
])

样本输出

/* 1 */
{
    "count" : 2,
    "values" : [
        "Sevilla",
        "ES",
        "Andalucía"
    ]
}

/* 2 */
{
    "count" : 1,
    "values" : [
        "London",
        "GB",
        "Greater London"
    ]
}

/* 3 */
{
    "count" : 1,
    "values" : [
        "Cádiz",
        "ES",
        "Andalucía"
    ]
}