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# \$1unset
<a name="unset-stage"></a>

8.0 版的新增内容

弹性集群不支持。

Amazon DocumentDB 中的`$unset`聚合阶段允许您从文档中删除字段。

**参数**
+ `expression`：字段名称或多个字段名称的列表。

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

以下示例演示了如何使用`$unset`聚合阶段来移除字`price`段。

**创建示例文档**

```
db.inventory.insertMany([
  { item: "pencil", quantity: 100, price: 0.24},
  { item: "pen", quantity: 204, price: 1.78 }
]);
```

**聚合示例**

```
db.inventory.aggregate([
  {
    $unset: "price"
  }
])
```

**输出**

```
[
  {
    _id: ObjectId('69248951d66dcae121d2950d'),
    item: 'pencil',
    quantity: 100
  },
  {
    _id: ObjectId('69248951d66dcae121d2950e'),
    item: 'pen',
    quantity: 204
  }
]
```

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

要查看使用该`$unset`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 example() {
  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 inventory = db.collection('inventory');

  const result = await inventory.aggregate([
      {
        $unset: "price"
      }
  ]).toArray();

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

example();
```

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

```
from pymongo import MongoClient

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

    result = list(inventory.aggregate([
      {
        "$unset": "price"
      }
    ]))

    print(result)
    client.close()

example()
```

------