如何将 mongo db 中的不同项目聚合到单独的数组中？

Question

我有一个 API 端点，它检查 mongo db 并以以下结构返回，例如：

{
  "Name": "Test"
  "Location": "Whatever",
  "customerServices": [
      {
        "id": "test",
        "cusId": "test",
        "serviceAdr": "test",
        "serviceCounty": "West",
        "name": "test"
      },
      {
        "id": "test",
        "cusId": "test",
        "serviceAdr": "test",
        "serviceCounty": "West",
        "name": "test"
      },
      {
        "id": "test",
        "cusId": "test",
        "serviceAdr": "test",
        "serviceCounty": "East",
        "name": "test"
      }
  ]
}

我想要做的是将聚合添加到管道中，这将创建额外的 field-serviceCounties并包含来自 customerServices 数组的不同serviceCounty 值。 如下所示：

{
  "Name": "Test"
  "Location": "Whatever",
  "customerServices": [
      {
        "id": "test",
        "cusId": "test",
        "serviceAdr": "test",
        "serviceCounty": "West",
        "name": "test"
      },
      {
        "id": "test",
        "cusId": "test",
        "serviceAdr": "test",
        "serviceCounty": "West",
        "name": "test"
      },
      {
        "id": "test",
        "cusId": "test",
        "serviceAdr": "test",
        "serviceCounty": "East",
        "name": "test"
      }
  ],
  "serviceCounties": [
    {
      "countyName":"East"
    },
    {
      "countyName":"West"
    }
] 
}

我尝试了以下方法，但没有奏效。 我缺少一些东西或做错了：

                'serviceCounties': {
                    '$reduce': {
                        'input': '$services.event.services',
                        'initialValue': [],
                        'in': [{
                            "countyName": { '$concatArrays': ["$$value.serviceCounty", "$$this"] }
                        }]
                    }
                }

任何想法如何做到这一点？

Answer 1

你可以试试这个。

db.collection.aggregate([
  {
    $addFields: {
      "serviceCounties": [
        {
          $map: {
            input: "$customerServices",
            in: {
              "countyName": "$$this.serviceCounty"
            }
          }
        }
      ]
    }
  }
])

操场

$addfields添加serviceCounties数组
$map以获取customerServices值。