批量发送电子邮件并捕获不成功的尝试

Question

前端代码包含一个名称列表，每个名称旁边都有复选框。目标是向所有被检查的姓名发送电子邮件。单击提交按钮时，会向我的后端发送一组 ID（针对每个用户）。

后端代码查询数据库（mongo 使用 mongoose odm）并找到用户。我需要在后端完成一些任务：

• 使用提供的 ID 数组查找用户
• 创建并向每个用户发送电子邮件
• 如果电子邮件发送成功，请更新数据库中用于发送电子邮件的文档字段
• 如果邮件失败，将用户名发回前端，通知“发件人”邮件尝试失败。

我在这段代码上工作的时间比我想承认的要长...这是我目前所拥有的（我担心后端代码）：

exports.sendEmailToUsers = function (req, res, next) {
  mongoose.model('SpendingReport').find({ _id: { $in: req.body.recipientIds } }).populate('report user')
    .find({ 'report.emailedReport': { $exists: false } })  // this needs to be refined for dev, new reports will have an emailedGradePost property
    .then(spendingReports => {
      return Bluebird.map(spendingReports, spendingReport => {
        const email = new Email({ email: spendingReport.user.email, name: spendingReport.user.fullName }, {})

        return email.send()
          .then(() => {
            spendingReport.report.update({ emailedReport: new Date() })
            // I don't need anything returned if it is successful, this feels weird though, map doesn't
            // seem like the  correct function to use.

            // return {spendingReport.report.emailedGradePost}
          })
          .catch(e => {
            // I am catching each email's error so I know which email failed
            return { error: e, user: spendingReport.user.fullName }
          });
      });
    })
    .then(unsuccessfulAttempts => {
      // the array has the error obect from the .catch and also undefined values for the successful attempts
      console.log(unsuccessfulAttempts);
    })
    .then(() => {
      res.sendStatus(200); //  filler status for now
    })
    .catch(e => {
      console.log(e);
    });
};

这是我的问题：

• 我正在使用Bluebird.map，这感觉就像代码的味道。理论上，我可以在包含来自数据库的一组文档的spendingReports 数组上使用.map，并使用来自每个spendingReport 的信息创建一封电子邮件。问题是，当我将电子邮件返回到承诺链中的下一个 .then() 时，我将无法访问 spendingReport 对象，例如

exports.sendEmailToUsers = function (req, res, next) {
  mongoose.model('SpendingReport').find({ _id: { $in: req.body.recipientIds } }).populate('report user')
    .find({ 'report.emailedReport': { $exists: false } })  // this needs to be refined for dev, new reports will have an emailedGradePost property
    .then(spendingReports => {
      return spendingReports.map(spendingReport => new Email({ email: spendingReport.user.email, name: spendingReport.user.fullName }, {}));
      // {email: email, spendingReport: spendingReport} I might need this format instead, referenect the note
      // in the next promise chain.
    })
    .then(emails => {
      return Bluebird.map(emails, email => {
        email.send()
          .then(() => {
            // Note: I lost access to "spendingReport", I would need to pass this object
            // with each email object {email: email, spendingReport: spendingReport}
            spendingReport.report.update({ emailedReport: new Date() })
              .catch(e => {
                return { error: e, user: spendingReport.user.fullName };
              })
          })
      })
    })
    .then(unsuccessfulAttempts => {

      console.log(unsuccessfulAttempts);
    })
    .then(() => {
      res.sendStatus(200); //  filler status for now
    })
    .catch(e => {
      console.log(e);
    });
};

• 我有一个嵌套的承诺链（在Bluebird.map 内，发送电子邮件，然后将其保存到成功的数据库中）。我知道嵌套承诺是一种反模式。减轻嵌套承诺的唯一方法是在每个.then 中传递与每封电子邮件关联的文档对象，与在Bluebird.map 中仅具有嵌套承诺链相比，这感觉更像是一种负担

  李>

• 当电子邮件成功并成功保存时，我不知道在Bluebird.map 中返回什么。现在我不返回任何东西，所以 undefined 被返回。

• 理想情况下，我可以并行发送所有电子邮件，例如Promise.all([email.send(), email.send(), email.send()])，但是，这使得将电子邮件成功保存到数据库更具挑战性（我需要再次访问spendingReports再次文档并更新report，这感觉就像很多查询）。

Answer 1

使用 async-await 可以减少您的问题（因为您可以通过索引获取所有项目）

async function(req, res, next) {
  let spendingReports = await mongoose.model('SpendingReport').find(...)
  let emails = spendingReports.map(r=>new Email(...))
  let sendingmails = emails.map(e=>e.send())
  let success=[],fail=[];
  await Promise.all(sendingmails.map((s,i)=>s.then(_=>success.push(i)).cache(_=>fail.push(i))))

  //now you have index of success and failed mails. 
  //just process these data and do whatever you want
}

---

中间数据不是必须的，比如这个单行（不要真的这样做）

async function(req, res, next) {
  let success=[],fail=[];
  await Promise.all(await mongoose.model('SpendingReport').find(...).then(spendingReports => spendingReports.map(r=>(new Email(...)).send().then(_=>success.push(r)).cache(_=>fail.push(r))))

  //now you have success and failed spendingReports. 
  //just process these data and do whatever you want
}