How can I handle MySQL queries in JavaScript with those asynchronous functions?

Question

could someone help me with my problem? I'm new to JavaScript (Node.js) and try to perform MySQL queries but this outputs nothing. I don't know how to handle this.

async function processArguments() {
    var result_customer = [];
    for(let i = 2; i < process.argv.length; ++i) {
        let sql = "SELECT Mandantennummer, Firmenname, VornameAnsp, NachnameAnsp, Telefonnummer, Strasse, PLZ"
                  "FROM kunde, item"
                  "WHERE kunde.K_ID=item.K_ID AND I_ID="+ process.argv[i];

        await link.query(sql, function(err_customer, customer, fields_customer) {
            if(err_customer) throw err_customer;
            result_customer.push(customer);
        });
    }

    for(let i = 0; i < result_customer.length; ++i) {
        console.log(result_customer[i].Firmenname);
    }

    link.end();
}

link.connect(function(err) {
    if(err) throw err;

    processArguments();
});

This outputs nothing

Thanks for help

Try to use this code:`link.connect(async function(err) { if(err) throw err; await processArguments(); });` — jvitoroc, Dec 08 '18 at 18:11
I guess you have hard coded it with a string instead of passing a value.Use object literals if you actually want to do this — Atul Agrawal, Dec 08 '18 at 18:20
I think there is something wrong with your sql query itself. Try to run it wither from mysql workbench or from terminal — Atul Agrawal, Dec 08 '18 at 18:22
What's the library? Is it `mysql`? Use promise-based libraries together with promises, — Estus Flask, Dec 08 '18 at 18:22
Possible duplicate of [How do I return the response from an asynchronous call?](https://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call) — nicholaswmin, Dec 08 '18 at 18:47

Aritra Chakraborty · Accepted Answer · 2018-12-08T18:55:04.653

You are using callback functions as Promise which will not work. You need to promisify the query.

async function processArguments() {
    var result_customer = [];
    for (let i = 2; i < process.argv.length; ++i) {
        let sql = "SELECT Mandantennummer, Firmenname, VornameAnsp, NachnameAnsp, Telefonnummer, Strasse, PLZ"
        "FROM kunde, item"
        "WHERE kunde.K_ID=item.K_ID AND I_ID=" + process.argv[i];

        const customer = await new Promise((resolve, rej) => {
            link.query(sql, function (err_customer, customer, fields_customer) {
                if (err_customer) rej(err_customer);
                resolve(customer);
            });
        });
        result_customer.push(customer);
    }
    link.end();
}

link.connect(function (err) {
    if (err) throw err;

    await processArguments();
});

If you want to await, it needs to be a Promise or an async function.

Edit: You can concat the process.argv[i] and use it along with IN in that query.

let sql = `SELECT Mandantennummer, Firmenname, VornameAnsp, NachnameAnsp, Telefonnummer, Strasse, PLZ 
FROM kunde, item 
WHERE kunde.K_ID=item.K_ID AND I_ID IN (${process.argv.slice(2).join(',')})`;

Yes, it works. I forgot async before function at connect – Grevak Dec 08 '18 at 19:16 — Grevak, Dec 08 '18 at 19:16

How can I handle MySQL queries in JavaScript with those asynchronous functions?

1 Answers1