在移动到另一个迭代之前等待内部循环

Question

我正在尝试使用函数通过 API 发送消息。当函数履行职责时，它返回一个值 messageLodId 并且需要在主循环中的 Attendence 处更新。但是当我执行此代码时，值未定义。

有两个问题：

1) 结构对吗？

2) 如果是，请提供此问题的答案。

//Posting SMS 
router.post('/sms/', async function(req, res) {
    let attendenceRecordId = parseInt(req.body.attendenceRecordId);
    let result = await AttendenceRecord.findOne({where: {id: attendenceRecordId }, include: [ {model: Attendence, include: [{model: Student}
    ]}, {
        model: Class
    }], order: [['date', 'DESC']]});

    if(!result) {
        res.sendStatus(404); 
    }

    for await (let attendence of result.attendences){

        let messageLogId = await sendSMS(attendence); 

        console.log("Message ID: ", messageLogId); 
        Attendence.update(
            { smsLogId: messageLogId },
            { where: { id: attendence.id  } }
          ); 
    }

    AttendenceRecord.update(
        { isMessageSent:true },
        { where: { id: result.id } }
      ); 

    res.send({messageSent: true});

});

这里是函数定义。现在我只返回 1 个。

在现实世界中，URL 返回一个代码。

async function sendSMS(attendence){

    //console.log(target);


    setTimeout(function(){
        let message = `Respected Parent, your son/daughter ${attendence.student.name} is absent on ${attendence.date}`;
        let messageURL = encodeURI(message); 
        let api = 'SOME VALUE';
        let phone = attendence.student.fphone.substring(1, 11); 
        let target = `http://BASE_URL/api.php?key=${api}&receiver=92${phone}&sender=DigitalPGS&msgdata=${messageURL}`; 

        return 1; 
    }, 2000); 


}

Answer 1

您应该从 sendSMS 返回承诺。在 setTimeout 回调函数中解析 promise。

function sendSMS(attendence){

    //console.log(target);
   return new Promise((resolve, reject) => {
   setTimeout(function(){
        let message = `Respected Parent, your son/daughter ${attendence.student.name} is absent on ${attendence.date}`;
        let messageURL = encodeURI(message); 
        let api = 'SOME VALUE';
        let phone = attendence.student.fphone.substring(1, 11); 
        let target = `http://BASE_URL/api.php?key=${api}&receiver=92${phone}&sender=DigitalPGS&msgdata=${messageURL}`; 

        resolve(1); 
    }, 2000); 
   });

}

Answer 2

你应该让 sendSMS 返回一个承诺，然后等待：

exec();

async function exec()
{
  var records = [1,2,3];

  for(var i=0;i<records.length;i++)
  {
     var messageLogId = await sendSMS(records[i]);
     console.log("Result received from resolve", messageLogId);
  }
}

function sendSMS(record)
{
    // simulate an async method:
    return new Promise(function(resolve, reject) {
      setTimeout(function() {
        console.log("Send sms for record", record);
        resolve(1);
      }, 1000);
    });
}

注意这里的setTimeout 只是为了演示一个异步操作。在现实世界中，您的 sendSMS 函数无疑会调用一个 API，该 API 本身是异步的 - 只需从中返回承诺（或者，如果 API 客户端不返回，则将调用包装在承诺中）。

Answer 3

首先，将您的函数设为Promisify。然后分块你的函数并在for 循环中调用该函数并使用Promise.all() 处理。

const manyPromises = [];

for (const attendence of result.attendences) {
  manyPromises.push(sendSmsAndUpdateStatus(attendence));
}
// Execution wait until all promises fulfilled/rejected
const result = await Promise.all(manyPromises);

const sendSmsAndUpdateStatus = async (attendence) => {
  try {
    const messageLogId = await sendSMS(attendence);
    const updateObj = { smsLogId: messageLogId };
    const condition = { where: { id: attendence.id } };
    const result = await Attendence.update(updateObj, condition);
    return { result, messageLogId };
  } catch (err) {
    logger.error(err);
    throw err;
  }
};

const sendSMS = (attendence) => {
  return new Promise((resolve) => {
    setTimeout(() => {
      const message = `Respected Parent, your son/daughter ${attendence.student.name} is absent on ${attendence.date}`;
      const messageURL = encodeURI(message);
      const api = 'SOME VALUE';
      const phone = attendence.student.fphone.substring(1, 11);
      const target = `http://BASE_URL/api.php?key=${api}&receiver=92${phone}&sender=DigitalPGS&msgdata=${messageURL}`;
      return resolve(1);
    }, 2000);
  });
};

总结确保您的函数sendSMS 将返回Promise，之后您可以使用async/await 或.then().catch() 方法处理它。