Promise not waiting for return value in NodeJS

Question

Hi as i am new to NodeJS as a follow-up to my previous question (Having problems getting new Array Value after looping in NodeJS) i have managed to get my code mostly working for parsing a list of email and querying them to the database, unable to get the return value in my promise when i get a response back from NodeJS API.

I am using MySQL 2.18.1 for my database and 4.17.1

Any idea i can solve it? Been trying it for a few hours.

Logs:

IM OUT HERE
Promise { { recipients: [] } }
{ recipients: [] }

retrieve_for_notification.js

async function processEmails(emails) {
    var retrieveValues = {
        recipients: []
    };

    // emails consist of those who were mentioned/notified, check condition whether they are eligible to be placed in receipients list
    for (var i = 0; i < emails.length; i++) {
        console.log(emails[i]);

        // 1 - check for suspended
        // 2 - check whether teacher and student pair is registered
        var sql1 = 'SELECT COUNT(*) as count_value FROM school.schoolinformation WHERE email = ? AND user_status = ?';
        var sql2 = 'SELECT COUNT(*) as count_value2 FROM school.registration_relationship WHERE teacher_email = ? AND student_email = ?';
        var sql3 = 'SELECT COUNT(*) as count_value3 FROM school.schoolinformation WHERE email = ? AND user_type = ?';

        var sqlvalues1 = [emails[i], 1];
        var sqlvalues2 = [teacher, emails[i]];
        var sqlvalues3 = [emails[i], 0];

        // check for suspended
        con.pool.query(sql1, sqlvalues1, async function (err1, result1) {
            if (err1) throw err1;
            var res1 = await getResult(sql1, sqlvalues1)
            // console.log("(1) res value is %s", res1[0].count_value);
            if (res1 > 0) return; // if result found skip to next email

            // check whether teacher and student pair is registered
            con.pool.query(sql2, sqlvalues2, async function (err2, result2) {
                if (err2) throw err2;
                var res2 = await getResult(sql2, sqlvalues2)

                // teacher and student pair is not registered
                if (res2 == 0) {
                    // check whether student mentioned is a valid student
                    con.pool.query(sql3, sqlvalues3, async function (err3, result3) {
                        if (err3) throw err3;
                        var res3 = await getResult(sql3, sqlvalues3)

                        // student is valid
                        if (res3 == 0) {
                            retrieveValues.recipients.push(sqlvalues3[0]);
                        }
                    });
                }
                else {
                    retrieveValues.recipients.push(sqlvalues2[0]);
                }
            });
        });
    };
    return recipientsList;
}

var recipientsList = processEmails(emails);

console.log("IM OUT HERE");
console.log(recipientsList);
// Resolve promise and response send, not using helper for this
var p2 = Promise.resolve(recipientsList);
p2.then(function(v) {
    console.log(v);
    response.write(JSON.stringify(v, null, 3));
    response.send.bind(response);
    response.end();
}, function(e) {
    console.error(e); // TypeError: Throwing
});

function getResult(sql, sqlvalues) {
    // console.log("getResult SQL Query: %s", sql);
    return new Promise(function (resolve, reject) {
        con.pool.query(sql, sqlvalues, function (err, result) {
            if (err) {
                reject(err)
            } else {
                resolve(result)
            }
        })
    })
}

It should be like this: https://nodejs.org/api/http.html#http_response_statuscode — Prerak Sola, Jan 31 '20 at 13:52
Depending on your express version it could be response.status = 2xx or response.status(2xx) https://stackoverflow.com/questions/10563644/how-to-specify-http-error-code — Julian Torregrosa, Jan 31 '20 at 13:53
Please specify (or confirm) which router framework you are using, and version. That will help to get the correct answer. :) — Eduardo Veras, Jan 31 '20 at 14:00
You have to replace `con.pool.query()` with a version that uses promises, not plain callbacks. Can't mix promises, `await` and plain async callbacks. Must use promises everywhere. If you use `require('mysql2/promise')`, then you will have [built-in promise support](https://www.npmjs.com/package/mysql2#using-promise-wrapper). — jfriend00, Jan 31 '20 at 15:35

score 0 · Answer 1 · answered Jan 31 '20 at 13:57

0

May by use - "response.statusCode = responseCode" for old version express

answered Jan 31 '20 at 13:57

ivani

13
4

i am using the latest express version 4.17.1 – dythe Jan 31 '20 at 14:00
recipientsList is not type of Response – ivani Jan 31 '20 at 14:16

Promise not waiting for return value in NodeJS

1 Answers1