MongoDB - 如何合并文档的字典字段？

Question

例如，我有一个如下所示的集合:

[{
    "_id": xxxx,
    "data": {
        "1": 10,
        "2": 30,
    }
},
{
    "_id": yyyy,
    "data": {
        "2": 10,
        "3": 30,
    }
}]

我想按键求和 data :

{
    "1": 10,
    "2": 40,
    "3": 30,
}

我该怎么做？

Answer 1

您可以尝试以下查询:

db.collection.aggregate([
    /** Convert data object into array of objects [{k:...,v:...}] */
    {
      $project: {
        data: {
          $objectToArray: "$data"
        }
      }
    },
    /** Unwind data array */
    {
      $unwind: "$data"
    },
    /** group on 'k' field of data field in each doc & sum values & push to 'v' field */
    {
      $group: {
        _id: "$data.k",
        v: {
          $sum: "$data.v"
        }
      }
    },
    /** Transform _id object as 'k' & v to 'v' of an object of array ([{k:...,v:...}]) &
     *  make an object of field named data */
    {
      $project: {
        _id: 0,
        data: {
          $arrayToObject: [
            [
              {
                k: "$_id",
                v: "$v"
              }
            ]
          ]
        }
      }
    },
    /** make data as new root to each doc */
    {
      $replaceRoot: {
        newRoot: "$data"
      }
    }
  ])

测试: MongoDB-Playground