适用对象:
MongoDB vCore
$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。
使用 $reverseArray
运算符的语法如下所示:
{
$reverseArray: <array>
}
说明 | |
---|---|
<array> |
要反转顺序的数组。 |
让我们通过以下示例 json 来了解用法。
{
"_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"
]
}
在聚合管道中反转 promotionEvents
数组的顺序。
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 } }
])
此查询将返回以下文档。
[
{
"_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 }
}
}
]
}
]