mongodb - 无法使用 $toString 将数字转换为字符串

Question

我正在研究 MongoDB(版本 4.0.0)聚合功能，但我无法使简单的 $toString 正常工作。当我删除 $toString 运算符时，我得到以下输出:

{ "_id" : ObjectId("5b4fa13c0ec5e844757333d5"), "payment_date" : 20180621, "payment_date_formatted" : 20180721 }
{ "_id" : ObjectId("5b4fa13c0ec5e844757333d7"), "payment_date" : 20180626, "payment_date_formatted" : 20180726 }

但是当我尝试转换字段 payment_date_formatted 时，一切都出错了，输出是:

{ "_id" : ObjectId("5b4fa13c0ec5e844757333d5"), "payment_date" : 20180621, "payment_date_formatted" : "2.01807e+07" }
{ "_id" : ObjectId("5b4fa13c0ec5e844757333d7"), "payment_date" : 20180626, "payment_date_formatted" : "2.01807e+07" }

为什么会这样？这是聚合调用:

db.payment_orders.aggregate([
  {
    "$match": {
      "company": ObjectId("5b368de558b52c13789edddd"),
      "payment_date": {
        "$gte": 20170601
      }
    }
  },
  {
    "$addFields": {
      "payment_date_formatted": {
        "$add": [
          "$payment_date",
          100
        ]
      }
    }
  },
  {
    "$project": {
      "payment_date": 1,
      "payment_date_formatted": {$toString: "$payment_date_formatted"}
    }
  }
]);

Answer 1

您需要使用 $toLong和 $toString同时在这里聚合

db.payment_orders.aggregate([
  {
    "$project": {
      "payment_date": { "$toLong": "$payment_date" },
      "payment_date_formatted": {
        "$toString": { "$toLong": "$payment_date_formatted" }
      }
    }
  }
])

可以试试here