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# $documentNumber
<a name="documentNumber"></a>

8.0.2 版中的新内容。

Amazon DocumentDB 中的`$documentNumber`窗口运算符根据`$setWindowFields`阶段`sortBy`顺序为其分区中的每个文档返回一个不同的序列号。与`$rank`和不同`$denseRank`，它不对关系进行特殊处理：每个文档都有一个唯一的编号（例如，`1, 2, 3, 4`），`sortBy`值相等的文档按照遇到的顺序进行编号。它是在`$setWindowFields`舞台的`output`字段下指定的。

它是一个仅在`$setWindowFields`舞台中使用的窗口运算符。

**参数**
+ `$documentNumber`将空文档`{}`作为其值。
+ 它不接受`window`框架。
+ 在`$setWindowFields`舞台中只需要一把`sortBy`钥匙。

## 示例（MongoDB Shell）
<a name="documentNumber-examples"></a>

以下示例按对文档进行分区`game`，按降序对每个分区进行`score`排序，并为每个玩家分配一个连续的文档编号。

**创建示例文档 **

```
db.players.insertMany([
  { _id: 1, game: "A", player: "Alice", score: 90 },
  { _id: 2, game: "A", player: "Bob", score: 85 },
  { _id: 3, game: "A", player: "Carol", score: 85 },
  { _id: 4, game: "A", player: "Dave", score: 70 },
  { _id: 5, game: "B", player: "Erin", score: 95 },
  { _id: 6, game: "B", player: "Frank", score: 80 }
]);
```

**查询示例 **

```
db.players.aggregate([
  {
    $setWindowFields: {
      partitionBy: "$game",
      sortBy: { score: -1 },
      output: {
        documentNumber: { $documentNumber: {} }
      }
    }
  }
]);
```

**输出**

```
[
  { "_id": 1, "game": "A", "player": "Alice", "score": 90, "documentNumber": 1 },
  { "_id": 2, "game": "A", "player": "Bob", "score": 85, "documentNumber": 2 },
  { "_id": 3, "game": "A", "player": "Carol", "score": 85, "documentNumber": 3 },
  { "_id": 4, "game": "A", "player": "Dave", "score": 70, "documentNumber": 4 },
  { "_id": 5, "game": "B", "player": "Erin", "score": 95, "documentNumber": 1 },
  { "_id": 6, "game": "B", "player": "Frank", "score": 80, "documentNumber": 2 }
]
```

在每个`game`分区中，每个玩家都会收到一个按降`score`序排列的不同序列号。Bob 和 Carol 并列`85`但仍处于编号`2`和`3`遭遇顺序排列。

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

要查看在`$setWindowFields`阶段中使用`$documentNumber`运算符的代码示例，请选择要使用的语言的选项卡：

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

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

async function example() {
  const client = new MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false');

  try {
    await client.connect();
    const db = client.db('test');
    const players = db.collection('players');

    await players.insertMany([
      { _id: 1, game: "A", player: "Alice", score: 90 },
      { _id: 2, game: "A", player: "Bob", score: 85 },
      { _id: 3, game: "A", player: "Carol", score: 85 },
      { _id: 4, game: "A", player: "Dave", score: 70 },
      { _id: 5, game: "B", player: "Erin", score: 95 },
      { _id: 6, game: "B", player: "Frank", score: 80 }
    ]);

    const result = await players.aggregate([
      {
        $setWindowFields: {
          partitionBy: "$game",
          sortBy: { score: -1 },
          output: {
            documentNumber: { $documentNumber: {} }
          }
        }
      }
    ]).toArray();

    console.log(result);
  } finally {
    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')

    try:
        db = client['test']
        players = db['players']

        players.insert_many([
            { '_id': 1, 'game': 'A', 'player': 'Alice', 'score': 90 },
            { '_id': 2, 'game': 'A', 'player': 'Bob', 'score': 85 },
            { '_id': 3, 'game': 'A', 'player': 'Carol', 'score': 85 },
            { '_id': 4, 'game': 'A', 'player': 'Dave', 'score': 70 },
            { '_id': 5, 'game': 'B', 'player': 'Erin', 'score': 95 },
            { '_id': 6, 'game': 'B', 'player': 'Frank', 'score': 80 }
        ])

        result = list(players.aggregate([
            {
                '$setWindowFields': {
                    'partitionBy': '$game',
                    'sortBy': { 'score': -1 },
                    'output': {
                        'documentNumber': { '$documentNumber': {} }
                    }
                }
            }
        ]))

        print(result)
    finally:
        client.close()

example()
```

------