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。

# \$1size
<a name="size-query"></a>

`$size` 查詢運算子會比對陣列欄位具有指定數量元素的文件。這適用於根據陣列長度篩選文件。

**參數**
+ `field`：要檢查的陣列欄位。
+ `count`：陣列必須包含的確切元素數量。

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

以下範例示範如何使用 `$size`運算子來尋找具有恰好三個標籤的所有產品。

**建立範例文件**

```
db.products.insertMany([
  { _id: 1, name: "Laptop", tags: ["electronics", "computers", "portable"] },
  { _id: 2, name: "Mouse", tags: ["electronics", "accessories"] },
  { _id: 3, name: "Desk", tags: ["furniture", "office", "workspace"] },
  { _id: 4, name: "Monitor", tags: ["electronics"] }
]);
```

**查詢範例**

```
db.products.find({ tags: { $size: 3 } });
```

**輸出**

```
{ "_id" : 1, "name" : "Laptop", "tags" : [ "electronics", "computers", "portable" ] }
{ "_id" : 3, "name" : "Desk", "tags" : [ "furniture", "office", "workspace" ] }
```

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

若要檢視使用`$size`查詢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('products');

  const result = await collection.find({ tags: { $size: 3 } }).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['products']

    result = list(collection.find({'tags': {'$size': 3}}))

    print(result)
    client.close()

example()
```

------