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

5.0 版的新增内容

弹性集群不支持。

`$dateDiff`聚合运算符以指定单位计算两个日期之间的差。它返回开始日期和结束日期之间跨越单位边界的数量。

**参数**
+ `startDate`：开始日期表达式。
+ `endDate`：结束日期表达式。
+ `unit`: 差异的时间单位。支持的单位是`year`、`quarter`、`month`、`week`、`day`、`hour`、`minute`、`second`、和`millisecond`。

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

以下示例演示如何使用`$dateDiff`运算符来计算从下单到交货之间的天数。

**创建示例文档**

```
db.shipments.insertMany([
  {
    orderId: 1001,
    orderDate: ISODate("2025-01-10T08:00:00Z"),
    deliveryDate: ISODate("2025-01-15T14:30:00Z")
  },
  {
    orderId: 1002,
    orderDate: ISODate("2025-02-05T10:00:00Z"),
    deliveryDate: ISODate("2025-02-12T16:45:00Z")
  }
]);
```

**查询示例**

```
db.shipments.aggregate([
  {
    $project: {
      orderId: 1,
      orderDate: 1,
      deliveryDate: 1,
      daysToDeliver: {
        $dateDiff: {
          startDate: "$orderDate",
          endDate: "$deliveryDate",
          unit: "day"
        }
      }
    }
  }
]);
```

**输出**

```
[
  {
    _id: ObjectId('6924a5f2d66dcae121d29517'),
    orderId: 1001,
    orderDate: ISODate('2025-01-10T08:00:00.000Z'),
    deliveryDate: ISODate('2025-01-15T14:30:00.000Z'),
    daysToDeliver: 5
  },
  {
    _id: ObjectId('6924a5f2d66dcae121d29518'),
    orderId: 1002,
    orderDate: ISODate('2025-02-05T10:00:00.000Z'),
    deliveryDate: ISODate('2025-02-12T16:45:00.000Z'),
    daysToDeliver: 7
  }
]
```

## 代码示例
<a name="dateDiff-code"></a>

要查看使用该`$dateDiff`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 shipments = db.collection('shipments');
  
  const result = await shipments.aggregate([
    {
      $project: {
        orderId: 1,
        orderDate: 1,
        deliveryDate: 1,
        daysToDeliver: {
          $dateDiff: {
            startDate: "$orderDate",
            endDate: "$deliveryDate",
            unit: "day"
          }
        }
      }
    }
  ]).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']
    shipments = db['shipments']
    
    result = list(shipments.aggregate([
        {
            "$project": {
                "orderId": 1,
                "orderDate": 1,
                "deliveryDate": 1,
                "daysToDeliver": {
                    "$dateDiff": {
                        "startDate": "$orderDate",
                        "endDate": "$deliveryDate",
                        "unit": "day"
                    }
                }
            }
        }
    ]))
    
    print(result)
    client.close()

example()
```

------