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

Amazon DocumentDB `$dayOfMonth` 中的彙總運算子會擷取指定日期的當月日期 （從 1 到 31)。此運算子適用於分組、篩選或擷取文件中日期欄位的月份日期。

**參數**
+ `date expression`：日期表達式可以是文件的日期欄位、日期物件或日期字串。

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

此範例示範如何使用 `$dayOfMonth` 運算子，從文件中的日期欄位中擷取當月的日期。

**建立範例文件**

```
db.events.insertMany([
  { _id: 1, eventDate: new Date("2022-01-15T12:00:00Z") },
  { _id: 2, eventDate: new Date("2022-02-28T15:30:00Z") },
  { _id: 3, eventDate: new Date("2022-03-01T09:45:00Z") },
  { _id: 4, eventDate: new Date("2022-04-30T23:59:59Z") }
]);
```

**查詢範例**

```
db.events.aggregate([
  { $project: {
    eventDay: { $dayOfMonth: "$eventDate" }
  }}
])
```

**輸出**

```
[
  { "_id" : 1, "eventDay" : 15 },
  { "_id" : 2, "eventDay" : 28 },
  { "_id" : 3, "eventDay" : 1 },
  { "_id" : 4, "eventDay" : 30 }
]
```

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

若要檢視使用 `$dayOfMonth`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 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 events = db.collection('events');

  const result = await events.aggregate([
    { $project: {
      eventDay: { $dayOfMonth: "$eventDate" }
    }}
  ]).toArray();

  console.log(result);
  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.mydatabase
    events = db.events

    result = list(events.aggregate([
        { "$project": {
            "eventDay": { "$dayOfMonth": "$eventDate" }
        }}
    ]))

    print(result)
    client.close()

example()
```

------