mysql - 如何修复发送到客户端后无法设置 header ？

Question

在过去 2.5 小时阅读了这个主题后，我无法确定如何解决我的问题:发送到客户端后无法设置 header 问题，但我认为这与底部的以下代码有关，尤其是代码以粗体显示。

任何帮助或协助将不胜感激。

app.post("/api/tracking/retrieve", (req, res) => {

res.setHeader('Content-Type', 'application/json'); 
// before all the iterations

    const trackingCodes = ['EZ6000000006', 'EZ4000000004'];
    const carrierCodes = ['UPS', 'UPS'];

    trackingCodes.forEach((trackingCode) => {
        carrierCodes.forEach((carrierCode) => {
            const tracker = new api.Tracker({
                tracking_code: trackingCode,
                carrier: carrierCode
            })

            tracker.save().then(function (data) {

                table = 'tracking_table';
                col = ['user_id', 'tracking_number'];
                val = [user_id, tracker.tracking_code];

            **// !ISSUE: :: ::: :::: ::::: :::::: ::::::: //**

                main.create(table, col, val, function (data) {
                      res.send(JSON.stringify({
                        id: "",
                        user_id: user_id,
                        tracking_number: data.tracking_code
                    })); // replace this for your res.json()
                });
            }

            )
                .catch(error => {
                    // handle errors
                    console.log('There has been an error with your submission.')
                });
        })
    })
res.end()
});

Answer 1

正如 @kiran Mathew 所回答的，res.json() 在 for 循环内被一次又一次调用，这就是为什么会发生“发送响应后无法设置 header ”的原因。

您可以使用结果数组“trackingNumbers”来存储所有tracking_number，然后退出循环，发送单个响应。

app.post("/api/tracking/retrieve", (req, res) => {
const trackingCodes = ["EZ6000000006", "EZ4000000004"];
  const carrierCodes = ["UPS", "UPS"];
  const trackingNumbers = [];

  trackingCodes.forEach(trackingCode => {
    carrierCodes.forEach(carrierCode => {
      const tracker = new api.Tracker({
        tracking_code: trackingCode,
        carrier: carrierCode
      });

      tracker
        .save()
        .then(function(data) {
          table = "tracking_table";
          col = ["user_id", "tracking_number"];
          val = [user_id, tracker.tracking_code];

          // !ISSUE: :: ::: :::: ::::: :::::: ::::::: //**

          main.create(table, col, val, function(data) {
            // res.json({
            //   id: "",
            //   user_id: user_id,
            //   tracking_number: data.tracking_code
            // });

            trackingNumbers.push(data.tracking_code);
          });
        })
        .catch(error => {
          // handle errors
          console.log("There has been an error with your submission.");
        });

      res.json({
        id: "",
        user_id: user_id,
        tracking_number: trackingNumbers
      });
    });
  });
});