db.command.aggregate.switch
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1. 操作符描述功能:根据给定的 switch-case-default
计算返回值、
声明:`db.command.aggregate.switch({ branches: [ case: <表达式>, then: <表达式>, case: <表达式>, then: <表达式>, ... ], default: <表达式> })
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2. 操作符参数字段 | 类型 | 必填 | 说明 |
---|---|---|---|
- | Object | 是 | switch-case-default 语句中各表达式可为任意聚合表达式 |
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3. 示例代码假设集合 items
的记录如下:
{ "_id": "0", "name": "item-a", "amount": 100 }{ "_id": "1", "name": "item-b", "amount": 200 }{ "_id": "2", "name": "item-c", "amount": 300 }
我们可以使用 switch
,根据 amount
字段,来生成新的字段 discount
:
// 云函数环境下示例代码const tcb = require('@cloudbase/node-sdk')const app = tcb.init({ env: 'xxx'})
const db = app.database()const $ = db.command.aggregateconst _ = db.command
exports.main = async (event, context) => { const res = await db .collection('items') .aggregate() .project({ name: 1, discount: $.switch({ branches: [ { case: $.gt(['$amount', 250]), then: 0.8 }, { case: $.gt(['$amount', 150]), then: 0.9 } ], default: 1 }) }) .end() console.log(res.data)}
输出如下:
{ "_id": "0", "name": "item-a", "discount": 1 }{ "_id": "1", "name": "item-b", "discount": 0.9 }{ "_id": "2", "name": "item-c", "discount": 0.8 }