如何在对 NodeJS 中的数据库进行多次异步调用的过程中发送响应？

Question

需要终止 POST 函数并发送 Error: something 作为响应，而不终止程序。

样本for-loop：

for (let i = 0; i < req.body.listoftouristsbyid.length; i++) {
  client.query("SELECT tourists.id FROM tourists WHERE tourists.id = " + req.body.listoftouristsbyid[i], function(err, result) {
    done();
    if (result.rows.length === 0) {
      console.log("Tourist " + req.body.listoftouristsbyid[i] + " you want to add does not exist");
      res.status(500);
      return res.render("Bad listoftoutistbyid request, student with id " + i + " does not exist");
    }
  })
}

我应该写什么来代替 return res.render，这样 POST 就不起作用，函数将终止并返回错误代码作为响应，但不会导致程序崩溃，这样我以后可以发送更多请求？

Answer 1

尝试使用 async.map 来解决您的问题。 for 循环不适用于异步函数。

async.map(
    req.body.listoftouristsbyid, 
    function(touristId, callback) {
        client.query("<query>", function(err, result) {
            if (result.rows.length === 0) {
                callback(new Error("not found"));
            }
            callback(null, result);
        });
    },
    function(err, result) {
        // send response here.
    } 
);

Answer 2

您可以为此使用 async-await，因为它在 Promise 和 Generators.

等异步调用处理程序中被广泛使用

这是一个示例代码：

app.post('/APIendpoint', async (req, res) => {

    let listoftouristsbyid      = req.body.listoftouristsbyid;

    let dbResult = [];

    // Can put this whole for loop inside try too. Then success response will also be inside try after for-loop
    for (let i = 0; i < listoftouristsbyid.length; i++) {

        try {
            let result = await callDB( "SELECT tourists.id FROM tourists WHERE tourists.id = " + listoftouristsbyid[i] );
            dbResult.push(result);
        }
        catch (err) {

            console.log("Tourist " + listoftouristsbyid[i] + " you want to add does not exist");

            res.status(500);
            return res.send("Bad listoftoutistbyid request, student with id " + i + " does not exist");

        }
    }

    console.log("Successfully fetched all records ", dbResult);

    res.status(200);
    return res.send(dbResult);

});

function callDB(query) {

    return new Promise ( (resolve, reject) => {
        client.query(query, function(err, result) {

            if (result.rows.length === 0) {
                reject("not found");
            } else {
                resolve(result.rows);
            }

        })
    });
}

如何在对 NodeJS 中的数据库进行多次异步调用的过程中发送响应？

How to send response in mid of multiple async calls to database in NodeJS?

javascript

node.js

express

ecmascript-6

ecmascript-2017