云函数无法提取到数据库内容?

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

cloud.init()

const db = cloud.database()

var OutPut={}

var total=0

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

    return new Promise((resolve, reject) => {

  const countResult = await db.collection('todo').count()
  total = countResult.total

       OutPut = { total: total }

       resolve(OutPut)

    })

}

但输出的total仍然是0。实际上数据库是有内容的。