为什么当我在 findOne 回调函数中将元素推送到数组中时，数组的值没有更新？

Question

这里有两个变量，它们的值对我来说是意想不到的，我无法解决它。每当我尝试将消息对象推送到循环内的数组中时，即使变量在循环的全局范围内，变量 currentUsersMessages 的值也是一个空数组，类似地 targetUserName 正在返回 undefined 但是我可以在回调函数中访问值。

    let AccountsCollection = require('../models/account')
    let {PrivateChat} = require('../models/chat.model')
    
    let messageFetchingLimit = 10;
     function standardMessage(message){

    let developedMessage = {
        content : message.content,
        content_received : message.content_received,
        content_seen : message.content_seen,
        sending_user : message.sending_user,
        receiving_user : message.receiving_user,
        delivery_date : message.delivery_date,
        delivery_time : message.delivery_time,
    }

    if(message.attachment !== undefined){
        developedMessage.attachment_url = `http://localhost:5000/chats/media/${message.attachment.file_name}`
        developedMessage.attachment_type = message.attachment.file_type
    }

    return developedMessage;

}
  

    router.get('/' ,  (req, res) => {
        let targetUserName;
        // Here We Will Find Target User Name to whom the logged in user is talking 
        
         AccountsCollection.findOne({identifier : {publicKey : req.query.targetUserPublicKey}} , (err,success) => {
            if(success){
                targetUserName = success.name
            }
            else {
                return null;
            }
        })
    
        // Here we will find and send previous chats of these chatting users
    
        const previousChats = []
        let currentUserMessages = []
        PrivateChat.findOne({ $and : [{'template.users' :{$in : req.query.userPublicKey}} , {'template.users' : {$in : req.query.targetUserPublicKey}}]}, async (err,usersChatObject) => {
                if (usersChatObject) {
                    const userPreviousChats = usersChatObject.template.messages
                    let previousMessageCount = parseInt(req.query.nfmr)
    
                    if(userPreviousChats.length > 0){
                    
                        //? IF Messages Are Less Than 10 
                    if((userPreviousChats.length - previousMessageCount) <= messageFetchingLimit ){
                        console.log('messages are less than 10')
                        for(let index = userPreviousChats.length - (previousMessageCount + 1) ; index >= 0; index--){
                            let message = await standardMessage(userPreviousChats[index])
                            currentUserMessages.push(message)
                            console.log(message)
                        
                        }
                        console.log(currentUserMessages)
                    }
                    //? IF Messages are not available
                    
                    else if (userPreviousChats.length < 1 || userPreviousChats.length == -1){
                        res.json({messageCount : 0})
                    }
                    
                    //? Otherwise if Messages are available and more than or equals to 10
                    
                    else {
                        let numberOfMessages = userPreviousChats.length - 1
                        let messageLeftToShow = numberOfMessages - previousMessageCount
                        
                        if(messageLeftToShow <= 10){
                            
                            for (let index = messageLeftToShow; index >= 0; index--) {
                                let message = standardMessage(userPreviousChats[index])
                                currentUserMessages.push(message)
                            }
                        }
                        else {
                            // If messages are more than 10
                            console.log(messageLeftToShow - 10);
                            for (let index = messageLeftToShow; index > messageLeftToShow - 10; index--) {
                                let message = standardMessage(userPreviousChats[index])
                                currentUserMessages.push(message)
                            }
                        }
                    }
    
                    previousChats.push({
                        userPublicKey : req.query.userPublicKey,
                        targetUserPublicKey : req.query.targetUserPublicKey,
                        targetName : targetUserName,
                        serverSentMessageCount : `${previousMessageCount + (currentUserMessages.length)}`,
                        messages : currentUserMessages
                    })
                    
                    console.log(previousChats)
                    res.json(previousChats)
                    
                }
                else {
                    res.json({error : "No Previous Messages Are Available"})
    
                    }
                }
                else {
                    console.log(err);
                    res.status(404).json({ error: 'Messages Record Is Not Available'})
                }
        })
    })

Answer 1

这里的问题是 AccountsCollection.findOne 和 PrivateChat.findOne 都是异步的

如果你用async/await而不是像这样的回调

来处理它会更容易

let AccountsCollection = require('../models/account')
let {
  PrivateChat
} = require('../models/chat.model')

let messageFetchingLimit = 10;


router.get('/', async(req, res) => {
  let targetUserName;
  // Here We Will Find Target User Name to whom the logged in user is talking 
  try {
    targetUserName = await AccountsCollection.findOne({
      identifier: {
        publicKey: req.query.targetUserPublicKey
      }
    })
  } catch (e) {
    targetUsername = null
  }

  // Here we will find and send previous chats of these chatting users

  const previousChats = []
  let currentUserMessages = []
  try {
    const userChatObject = await PrivateChat.findOne({
      $and: [{
        'template.users': {
          $in: req.query.userPublicKey
        }
      }, {
        'template.users': {
          $in: req.query.targetUserPublicKey
        }
      }]
    })
    const userPreviousChats = usersChatObject.template.messages
    let previousMessageCount = parseInt(req.query.nfmr)

    if (userPreviousChats.length > 0) {

      //? IF Messages Are Less Than 10 
      if ((userPreviousChats.length - previousMessageCount) <= messageFetchingLimit) {
        console.log('messages are less than 10')
        for (let index = userPreviousChats.length - (previousMessageCount + 1); index >= 0; index--) {
          let message = await standardMessage(userPreviousChats[index])
          currentUserMessages.push(message)
          console.log(message)

        }
        console.log(currentUserMessages)
      }
      //? IF Messages are not available
      else if (userPreviousChats.length < 1 || userPreviousChats.length == -1) {
        res.json({
          messageCount: 0
        })
        return;
      }

      //? Otherwise if Messages are available and more than or equals to 10
      else {
        let numberOfMessages = userPreviousChats.length - 1
        let messageLeftToShow = numberOfMessages - previousMessageCount

        if (messageLeftToShow <= 10) {

          for (let index = messageLeftToShow; index >= 0; index--) {
            let message = standardMessage(userPreviousChats[index])
            currentUserMessages.push(message)
          }
        } else {
          // If messages are more than 10
          console.log(messageLeftToShow - 10);
          for (let index = messageLeftToShow; index > messageLeftToShow - 10; index--) {
            let message = standardMessage(userPreviousChats[index])
            currentUserMessages.push(message)
          }
        }
      }

      previousChats.push({
        userPublicKey: req.query.userPublicKey,
        targetUserPublicKey: req.query.targetUserPublicKey,
        targetName: targetUserName,
        serverSentMessageCount: `${previousMessageCount + (currentUserMessages.length)}`,
        messages: currentUserMessages
      })

      console.log(previousChats)
      res.json(previousChats)

    } else {
      res.json({
        error: "No Previous Messages Are Available"
      })

    }
  } catch (err) {
    console.log(err);
    res.status(404).json({
      error: 'Messages Record Is Not Available'
    })
  }
})

为什么当我在 findOne 回调函数中将元素推送到数组中时，数组的值没有更新？

Why the values of array are not updating when I push elements in it in findOne callback function?

javascript

arrays

asynchronous

mongoose