通过

$reverseArray

$reverseArray 运算符用于反转数组中元素的的顺序。 在需要按相反顺序处理或显示数组元素时，此运算符适用。 其是一个数组表达式运算符，可以在聚合管道中使用。

语法

{
  $reverseArray: <array>
}

参数

参数 说明
<array> 要反转顺序的数组。

Example

让我们了解 stores 数据集中的示例 json 的用法。

{
  "_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5",
  "name": "Lakeshore Retail | DJ Equipment Stop - Port Cecile",
  "location": {
    "lat": 60.1441,
    "lon": -141.5012
  },
  "staff": {
    "totalStaff": {
      "fullTime": 2,
      "partTime": 0
    }
  },
  "sales": {
    "salesByCategory": [
      {
        "categoryName": "DJ Headphones",
        "totalSales": 35921
      }
    ],
    "fullSales": 3700
  },
  "promotionEvents": [
    {
      "eventName": "Bargain Blitz Days",
      "promotionalDates": {
        "startDate": {
          "Year": 2024,
          "Month": 3,
          "Day": 11
        },
        "endDate": {
          "Year": 2024,
          "Month": 2,
          "Day": 18
        }
      },
      "discounts": [
        {
          "categoryName": "DJ Turntables",
          "discountPercentage": 18
        },
        {
          "categoryName": "DJ Mixers",
          "discountPercentage": 15
        }
      ]
    },
    {
      "eventName": "Discount Delight Days",
      "promotionalDates": {
        "startDate": {
          "Year": 2024,
          "Month": 5,
          "Day": 11
        },
        "endDate": {
          "Year": 2024,
          "Month": 5,
          "Day": 18
        }
      }
    }
  ],
  "tag": [
    "#ShopLocal",
    "#FashionStore",
    "#SeasonalSale",
    "#FreeShipping",
    "#MembershipDeals"
  ]
}

示例 1：反转数组的顺序

聚合管道演示了运算符在数组顺序 promotionEvents 上执行反转的用法。

db.stores.aggregate([
    //filtering to one document
    {
      $match: {
        "_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5"
      }
    },
    {
      $project: {
        _id: 1,
        name: 1,
        promotionEventsReversed: { $reverseArray: "$promotionEvents" }
      }
    },
    // Include only _id, name, promotionalDates and eventName fields in the output 
    { $project: { _id: 1, name: 1 , "promotionEventsReversed.promotionalDates":1, "promotionEventsReversed.eventName":1  } } 
])

该查询返回具有提升Events 的反向顺序的文档。

  {
    "_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5",
    "name": "Lakeshore Retail | DJ Equipment Stop - Port Cecile",
    "promotionEventsReversed": [
      {
        "eventName": "Discount Delight Days",
        "promotionalDates": {
          "startDate": { "Year": 2024, "Month": 5, "Day": 11 },
          "endDate": { "Year": 2024, "Month": 5, "Day": 18 }
        }
      },
      {
        "eventName": "Bargain Blitz Days",
        "promotionalDates": {
          "startDate": { "Year": 2024, "Month": 3, "Day": 11 },
          "endDate": { "Year": 2024, "Month": 2, "Day": 18 }
        }
      }
    ]
  }

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