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$ROOT

Amazon DocumentDB 中的$ROOT运算符用于引用聚合管道中的整个输入文档。它允许您访问和操作完整的文档，包括其所有嵌套字段和结构。

参数

无

示例（MongoDB 外壳）

此示例演示$ROOT如何使用创建审核日志，该日志可捕获完整的原始文档以及有关文档处理时间的元数据。

创建示例文档

db.orders.insertMany([
  {
    _id: 1,
    orderId: "ORD-2024-001",
    customer: "María García",
    email: "maría@example.com",
    items: [
      { product: "Laptop", quantity: 1, price: 1299.99 }
    ],
    totalAmount: 1299.99
  },
  {
    _id: 2,
    orderId: "ORD-2024-002",
    customer: "Arnav Desai",
    email: "arnav@example.com",
    items: [
      { product: "Mouse", quantity: 2, price: 29.99 },
      { product: "Keyboard", quantity: 1, price: 89.99 }
    ],
    totalAmount: 149.97
  }
]);

查询示例

db.orders.aggregate([
  {
    $project: {
      processedAt: new Date(),
      originalDocument: "$$ROOT",
      summary: {
        $concat: [
          "Order ",
          "$orderId",
          " for ",
          "$customer",
          " - Total: $",
          { $toString: "$totalAmount" }
        ]
      }
    }
  }
]);

输出

[
  {
    _id: 1,
    processedAt: ISODate('2025-11-24T20:43:51.492Z'),
    originalDocument: {
      _id: 1,
      orderId: 'ORD-2024-001',
      customer: 'María García',
      email: 'maría@example.com',
      items: [ { product: 'Laptop', quantity: 1, price: 1299.99 } ],
      totalAmount: 1299.99
    },
    summary: 'Order ORD-2024-001 for María García - Total: $1299.99'
  },
  {
    _id: 2,
    processedAt: ISODate('2025-11-24T20:43:51.492Z'),
    originalDocument: {
      _id: 2,
      orderId: 'ORD-2024-002',
      customer: 'Arnav Desai',
      email: 'arnav@example.com',
      items: [
        { product: 'Mouse', quantity: 2, price: 29.99 },
        { product: 'Keyboard', quantity: 1, price: 89.99 }
      ],
      totalAmount: 149.97
    },
    summary: 'Order ORD-2024-002 for Arnav Desai - Total: $149.97'
  }
]

代码示例

要查看使用该$ROOT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');

async function createAuditLog() {
  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 orders = db.collection('orders');

  const result = await orders.aggregate([
    {
      $project: {
        processedAt: new Date(),
        originalDocument: "$$ROOT",
        summary: {
          $concat: [
            "Order ",
            "$orderId",
            " for ",
            "$customer",
            " - Total: $",
            { $toString: "$totalAmount" }
          ]
        }
      }
    }
  ]).toArray();

  console.log(result);
  await client.close();
}

createAuditLog();

Python

from pymongo import MongoClient
from datetime import datetime

def create_audit_log():
    client = MongoClient('mongodb://username:password@docdb-cluster.cluster-123456789.us-east-1.docdb.amazonaws.com:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
    db = client['test']
    collection = db['orders']

    result = list(collection.aggregate([
        {
            '$project': {
                'processedAt': datetime.now(),
                'originalDocument': '$$ROOT',
                'summary': {
                    '$concat': [
                        "Order ",
                        "$orderId",
                        " for ",
                        "$customer",
                        " - Total: $",
                        { '$toString': "$totalAmount" }
                    ]
                }
            }
        }
    ]))

    print(result)
    client.close()

create_audit_log()