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

8.0 版的新功能

Elastic 叢集不支援。

Amazon DocumentDB `$replaceWith` 中的彙總階段用於將輸入文件取代為新文件。輸入文件上的所有現有欄位，包括 \$1id 欄位，都會被新文件取代。 `$replaceWith` 通常用來扁平化文件，或將內嵌文件提升至頂層。

**參數**
+ `<replacement>` （必要）：將取代現有文件的新文件。

## 範例 (MongoDB Shell)
<a name="replaceWith-examples"></a>

下列範例示範如何使用 `$replaceWith`運算子取代 Amazon DocumentDB 集合中的現有文件。

**建立範例文件**

```
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 ]
  }
]);
```

**查詢範例**

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

**輸出**

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

## 程式碼範例
<a name="replaceWith-code"></a>

若要檢視使用 `$replaceWith`命令的程式碼範例，請選擇您要使用的語言標籤：

------
#### [ 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()
```

------