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# \$1replaceRoot
<a name="replaceRoot"></a>

该`$replaceRoot`运算符用于将根文档替换为指定的嵌入式文档。当您想要将嵌套文档提升到顶层或重构数据输出时，这很有用。

**参数**
+ `newRoot`：将替换现有根文档的新根文档。

## 示例（MongoDB 外壳）
<a name="replaceRoot-examples"></a>

此示例说明如何从买家订单中提取配送地址信息，这对于生成发货标签或地址列表非常有用。

**创建示例文档**

```
db.orders.insertMany([
  {
    "_id":1, "orderId": "ORD-2024-001", "customerId": "CUST-12345", "orderDate": "2024-01-15", "shippingAddress": { "name": "María García", "street": "123 Main St", "city": "Seattle", "state": "WA", "zipCode": "98101", "country": "USA" },"totalAmount": 149.99 },
  { "_id":2, "orderId": "ORD-2024-002", "customerId": "CUST-67890", "orderDate": "2024-01-16", "shippingAddress": { "name": "Arnav Desai", "street": "456 Oak Ave", "city": "Portland", "state": "OR", "zipCode": "97201", "country": "USA" }, "totalAmount": 89.50 } ])
```

**查询示例**

```
db.orders.aggregate([
  {
    $replaceRoot: {
      newRoot: "$shippingAddress"
    }
  }
])
```

**输出**

```
{
    name: 'María García',
    street: '123 Main St',
    city: 'Seattle',
    state: 'WA',
    zipCode: '98101',
    country: 'USA'
  },
  {
    name: 'Arnav Desai',
    street: '456 Oak Ave',
    city: 'Portland',
    state: 'OR',
    zipCode: '97201',
    country: 'USA'
  }
```

## 代码示例
<a name="replaceRoot-code"></a>

要查看使用该`$replaceRoot`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 extractShippingAddresses() {
  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('orders');

  const result = await collection.aggregate([
    {
      $replaceRoot: {
        newRoot: "$shippingAddress"
      }
    }
  ]).toArray();

  console.log(result);

  await client.close();
}

extractShippingAddresses();
```

------
#### [ Python ]

```
from pymongo import MongoClient

def extract_shipping_addresses():
    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['orders']

    result = list(collection.aggregate([
        {
            "$replaceRoot": {
                "newRoot": "$shippingAddress"
            }
        }
    ]))

    print(result)

    client.close()

extract_shipping_addresses()
```

------