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db.command.aggregate.switch

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> })

2. 操作符参数#

字段类型必填说明
-Objectswitch-case-default 语句中各表达式可为任意聚合表达式

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 }