// 云函数入口文件

const cloud = require('wx-server-sdk')

cloud.init()

const db=cloud.database()

const _ =db.command

const $ =_.aggregate

// 云函数入口函数

exports.main = async (event, context) => {

return await db.collection('class').aggregate()

.lookup({

    from: 'student',

    pipeline:$.pipeline()

.group({

    _id: null,

    score: $.avg('$score') //计算平均成绩

})

.done(),//表示结束定义

    as: 'stu',

  })

  .match({

    teacher:"徐老师"

})

.replaceRoot({

    newRoot: $.mergeObjects([ $.arrayElemAt(['$stu', 0]), '$$ROOT' ])

  }).project({

    _id:0,

    teacher:1,

    score:1,

  }).then(res=>{

    console.log('这是云函数里面的结果',res)

  })

  .end()

}

失败的是这样的提示

调用状态
失败, ret code 1
返回结果
{"errorCode":1,"errorMessage":"user code exception caught","stackTrace":"TypeError: db.collection(...).aggregate(...).lookup(...).match(...).replaceRoot(...).project(...).then is not a function\n    at Runtime.exports.main [as handler] (/var/user/index.js:33:6)\n    at Runtime.handleOnce (/var/runtime/node12/Runtime.engine.js:219:23)\n    at Timeout._onTimeout (/var/runtime/node12/Runtime.engine.js:56:12)\n    at listOnTimeout (internal/timers.js:549:17)\n    at processTimers (internal/timers.js:492:7)","statusCode":430}