根据主文档中的值，仅从子文档中检索某些字段

Question

我的mongodb中有一个收藏，如下所示

{
_id: ObjectId("5fa917baffdd553806e96ca4"),
priority: 1,
fields: {
    1: {
        id: NumberInt("1"),
        value: NumberInt("1"),
        label: "Din 1",
        dimension: null,
        valueHuman: "1"
    },
    9: {
        id: NumberInt("9"),
        value: NumberInt("259"),
        label: "",
        dimension: "",
        valueHuman: ""
    }
   }
  }

我要做的是根据优先级的值（如我应该得到的）获取字段

{
_id: ObjectId("5fa917baffdd553806e96ca4"),
priority: 1,
fields: {
    1: {
        id: NumberInt("1"),
        value: NumberInt("1"),
        label: "Din 1",
        dimension: null,
        valueHuman: "1"
    }
   }
  }

Answer 1

• $objectToArray将字段对象转换为数组

db.collection.aggregate([
  {
    $addFields: {
      fields: {
        $arrayToObject: {
          $filter: {
            input: { $objectToArray: "$fields" },
            cond: {
              $eq: [{ $toInt: "$$this.k" }, "$priority"]
            }
          }
        }
      }
    }
  }
])

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