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

8.0 版的新增内容

弹性集群不支持。

Amazon DocumentDB 中的`$replaceWith`聚合阶段用于将输入文档替换为新文档。输入文档上的所有现有字段（包括 \$1id 字段）都将替换为新文档。 `$replaceWith`通常用于扁平化文档或将嵌入式文档提升到顶层。

**参数**
+ `<replacement>`（必填）：将取代现有文档的新文档。

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

以下示例演示如何使用`$replaceWith`运算符替换 Amazon DocumentDB 集合中的现有文档。

**创建示例文档**

```
db.restaurants.insertMany([
  {
    "restaurantId": "REST-0Y9GL0",
    "name": "Biryani Adda",
    "cuisine": "Indian",
    "ratings": [ 3, 4, 3, 2, 2, 4, 1, 5, 5, 5 ]
  },
  {
    "restaurantId": "REST-8L2PX9",
    "name": "The Burger Spot",
    "cuisine": "American",
    "ratings": [ 2, 3, 4, 5, 3, 1, 1, 2, 4 ]
  }
]);
```

**查询示例**

```
db.restaurants.aggregate([
  { $replaceWith: {
      name: "$name",
      cuisine: "$cuisine",
      rating: { $avg: "$ratings" }
    }
  }
]);
```

**输出**

```
[
  {
    name: 'Biryani Adda',
    cuisine: 'Indian',
    rating: 3.4
  },
  {
    name: 'The Burger Spot',
    cuisine: 'American',
    rating: 2.7777777777777777
  }
]
```

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

要查看使用该`$replaceWith`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 replaceDoc() {
  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('restaurants');

  const result = await collection.aggregate([
    { $replaceWith: {
        name: "description_index",
        cuisine: 2,
        rating: { $avg: "$ratings" }
      }
    }
  ]).toArray();

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

replaceDoc();
```

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

```
from pymongo import MongoClient


def replace_document():
    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.restaurants

    result = list(collection.aggregate([
        {
            '$replaceWith': {
                'name': "$name",
                'cuisine': "$cuisine",
                'rating': { '$avg': "$ratings"}
            }
        }
    ]))

    print(result)
    client.close()

replace_document()
```

------