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$addFields

Amazon DocumentDB 聚合管道中的$addFields阶段允许您向文档添加新的计算字段。这对于向文档中添加派生或转换后的数据非常有用。

参数

示例（MongoDB 外壳）

以下示例演示$addFields如何使用添加新字段TotalInventory，该字段根据Inventory.OnHand和Inventory.OrderQnty字段计算总库存。

创建示例文档

db.example.insertMany([
  {
    "Item": "Spray Paint",
    "Colors": ["Black", "Red", "Green", "Blue"],
    "Inventory": {
      "OnHand": 47,
      "MinOnHand": 50,
      "OrderQnty": 36
    },
    "UnitPrice": 3.99
  },
  {
    "Item": "Ruler",
    "Colors": ["Red", "Green", "Blue", "Clear", "Yellow"],
    "Inventory": {
      "OnHand": 47,
      "MinOnHand": 40
    },
    "UnitPrice": 0.89
  }
]);

查询示例

db.example.aggregate([
  {
    $addFields: {
      TotalInventory: { $add: ["$Inventory.OnHand", "$Inventory.OrderQnty"] }
    }
  }
])

输出

[
  {
    "_id" : ObjectId("5bedafbcf65ff161707de24f"),
    "Item" : "Ruler",
    "Colors" : [ "Red", "Green", "Blue", "Clear", "Yellow" ],
    "Inventory" : {
      "OnHand" : 47,
      "MinOnHand" : 40
    },
    "UnitPrice" : 0.89,
    "TotalInventory" : 47
  },
  {
    "_id" : ObjectId("5bedafbcf65ff161707de250"),
    "Item" : "Spray Paint",
    "Colors" : [ "Black", "Red", "Green", "Blue" ],
    "Inventory" : {
      "OnHand" : 47,
      "MinOnHand" : 50,
      "OrderQnty" : 36
    },
    "UnitPrice" : 3.99,
    "TotalInventory" : 83
  }
]

代码示例

要查看使用该$addFields命令的代码示例，请选择要使用的语言的选项卡：

Node.js

const { MongoClient } = require('mongodb');

const client = await MongoClient.connect('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false');
const db = client.db('test');
const collection = db.collection('example');

const result = await collection.aggregate([
  {
    $addFields: {
      TotalInventory: { $add: ['$Inventory.OnHand', '$Inventory.OrderQnty'] }
    }
  }
]).toArray();

console.log(result);

await client.close();

Python

from pymongo import MongoClient

client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
db = client['test']
collection = db['example']

result = list(collection.aggregate([
    {
        '$addFields': {
            'TotalInventory': { '$add': ['$Inventory.OnHand', '$Inventory.OrderQnty'] }
        }
    }
]))

print(result)
client.close()