javascript - (Mongo/Mongoose) 如何处理等待多个查询结果

Question

我正在编写一个 Discord 机器人，该机器人每周生成文本和语音 channel 使用情况的公会统计数据。我的代码将多个 Mongo 查询分为不同的方法:

function getTopActiveTextChannels() {
  let topTextChannels = []
  ChannelModel.find({}).sort({"messageCountThisWeek": -1}).limit(topLimit)
   .exec(channels => {
    channels.forEach(c => {
      topTextChannels.push({"name": c.name, "messageCount": c.messageCount})
    })
    console.log(topTextChannels)
    return topTextChannels
  })
}

function getTopActiveVoiceMembers() {
  let topVoiceMembers = []
  UserModel.find({}).sort({"timeSpentInVoice": -1}).limit(topLimit)
  .exec(users => {
    users.forEach(u => {
      topVoiceMembers.push({"username": u.username, "timeSpentInVoice": u.timeSpentInVoice})
    })
    console.log(topVoiceMembers)
    return topVoiceMembers
  })
}

然后我有一种方法可以调用这两个方法并(目前)将值打印到控制台:

function getWeeklyGuildStats(client) {
  let topActiveTextChannels = getTopActiveTextChannels()
  let topVoiceMembers = getTopActiveVoiceMembers()
  let promisesArray = [topActiveTextChannels, topVoiceMembers]

  Promise.all(promisesArray).then(values => {console.log(values)})
}

执行getWeeklyGuildStats(client)输出:[ undefined, undefined ]。我确信我没有正确使用 promise ，但是当我遵循 Mongoose 的文档时，它告诉我使用 exec() 而不是 then()，但我得到了channels = null 错误。

有人会想到什么吗？这似乎是一个相当常见的模式。有谁有如何用单一方法解决多个 Mongoose 查询的解决方案吗？

Answer 1

Promise.all 应该接受一个 Promise 数组，而您的函数返回普通数组，因此您需要在获取用户和 channel 的帮助器方法中返回整个查询，然后执行您的操作promise.all

之后的逻辑

你的函数可能看起来像这样

function getTopActiveTextChannels() {
  return ChannelModel.find({}).sort({"messageCountThisWeek": -1}).limit(topLimit).exec();
}

function getTopActiveVoiceMembers() {
  return UserModel.find({}).sort({"timeSpentInVoice": -1}).limit(topLimit).exec();
}

那么调用这两个方法的函数将类似于

function getWeeklyGuildStats(client) {
  let topActiveTextChannels = getTopActiveTextChannels()
  let topVoiceMembers = getTopActiveVoiceMembers()
  let promisesArray = [topActiveTextChannels, topVoiceMembers]

  Promise.all(promisesArray).then(values => {
     console.log(values);
     // here you could do your own logic, the for loops you did in the helper methods before
  });
}