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

8.0 版的新增内容

弹性集群不支持。

Amazon DocumentDB 中的`$dateTrunc`聚合运算符将日期截断为指定单位。

**参数**
+ `date`：解析为日期或时间戳的日期表达式。
+ `unit`：一个字符串，它为子集表达式指定时间单位。支持的单位是`year`、`quarter`、`month`、`week`、`day`、`hour`、`minute`、`second`、和`millisecond`。

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

以下示例演示如何使用`$dateTrunc`运算符将日期截断为小时。

**创建示例文档**

```
db.events.insertMany([
  {
    eventName: "Event 1",
    eventTime: ISODate("2025-04-01T12:15:00Z")
  },
  {
    eventName: "Event 2",
    eventTime: ISODate("2025-08-15T14:33:22Z")
  },
]);
```

**查询示例**

```
db.events.aggregate([
  {
    $project: {
      eventName: 1,
      eventTime: 1,
      truncatedToHour: {
        $dateTrunc: {
          date: "$eventTime",
          unit: "hour"
        }
      }
    }
  }
]);
```

**输出**

```
[
  {
    _id: ObjectId('6924a258d66dcae121d29515'),
    eventName: 'Event 1',
    eventTime: ISODate('2025-04-01T12:15:00.000Z'),
    truncatedToHour: ISODate('2025-04-01T12:00:00.000Z')
  },
  {
    _id: ObjectId('6924a258d66dcae121d29516'),
    eventName: 'Event 2',
    eventTime: ISODate('2025-08-15T14:33:22.000Z'),
    truncatedToHour: ISODate('2025-08-15T14:00:00.000Z')
  }
]
```

## 代码示例
<a name="dateTrunc-code"></a>

要查看使用该`$dateTrunc`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 events = db.collection('events');
  
  const result = await events.aggregate([
    {
      $project: {
        eventName: 1,
        eventTime: 1,
        truncatedToHour: {
          $dateTrunc: {
            date: "$eventTime",
            unit: "hour"
          }
        }
      }
    }
  ]).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']
    events = db['events']
    
    result = list(events.aggregate([
        {
            "$project": {
                "eventName": 1,
                "eventTime": 1,
                "truncatedToHour": {
                    "$dateTrunc": {
                        "date": "$eventTime",
                        "unit": "hour"
                    }
                }
            }
        }
    ]))
    
    print(result)
    client.close()

example()
```

------