本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。

# \$1slice
<a name="slice-projection"></a>

`$slice` 投影運算子會限制查詢結果中傳回的陣列元素數目。它可讓您從陣列欄位的開頭或結尾擷取特定數量的元素，而無需載入整個陣列。

**參數**
+ `field`：要投影的陣列欄位。
+ `count`：要傳回的元素數目。正值會從開頭傳回元素，從結尾傳回負值。

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

下列範例示範如何使用`$slice`投影運算子，只傳回陣列欄位中的前兩個項目。

**建立範例文件**

```
db.inventory.insertMany([
  { _id: 1, item: "notebook", tags: ["office", "school", "supplies", "writing"] },
  { _id: 2, item: "pen", tags: ["office", "writing"] },
  { _id: 3, item: "folder", tags: ["office", "supplies", "storage", "organization"] }
]);
```

**查詢範例**

```
db.inventory.find(
  {},
  { item: 1, tags: { $slice: 2 } }
)
```

**輸出**

```
{ "_id" : 1, "item" : "notebook", "tags" : [ "office", "school" ] }
{ "_id" : 2, "item" : "pen", "tags" : [ "office", "writing" ] }
{ "_id" : 3, "item" : "folder", "tags" : [ "office", "supplies" ] }
```

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

若要檢視使用`$slice`投影運算子的程式碼範例，請選擇您要使用的語言標籤：

------
#### [ Node.js ]

```
const { MongoClient } = require('mongodb');

async function 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 collection = db.collection('inventory');

  const result = await collection.find(
    {},
    { projection: { item: 1, tags: { $slice: 2 } } }
  ).toArray();

  console.log(JSON.stringify(result, null, 2));
  await 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']
    collection = db['inventory']

    result = list(collection.find(
        {},
        {'item': 1, 'tags': {'$slice': 2}}
    ))

    print(result)
    client.close()

example()
```

------