SQL failed to output parameters - mysql

Question

So we have 2 tables:
listings
users
Currently, i'm trying to retrieve all the information of the given users id where the fk_poster_id of the listings table is the foreign key with reference made to the users id by using the GET method.But when i try to execute the codes, i receive [] as the output. Is there a way to solve this?
Here's my current sql codes
DROP DATABASE snapsell;
CREATE DATABASE IF NOT EXISTS `snapsell`;
USE `snapsell`;
DROP TABLE IF EXISTS `users`;
DROP TABLE IF EXISTS `listings`;
CREATE TABLE users (
id INT AUTO_INCREMENT PRIMARY KEY,
username VARCHAR(50) NOT NULL,
UNIQUE (username),
profile_pic_url VARCHAR(1000) NOT NULL,
created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
) ENGINE=INNODB;
-- THESE ARE JUST EXAMPLES AND TEST KITS.TO BE REMOVED BEFORE PRESENTATION.
INSERT INTO users (username, profile_pic_url) VALUES
("steve_jobs","https://upload.wikimedia.org/wikipedia/commons/thumb/f/f5/Steve_Jobs_Headshot_2010-CROP2.jpg/800px-Steve_Jobs_Headshot_2010-CROP2.jpg"),
("barack_obama","https://upload.wikimedia.org/wikipedia/commons/e/e9/Official_portrait_of_Barack_Obama.jpg"),
("kim_jung_un","https://upload.wikimedia.org/wikipedia/commons/d/d0/Kim_Jung-Un_-_Inter_Korean_Summit%28cropped%29_v1.jpg"),
("lee_kuan_yew","https://upload.wikimedia.org/wikipedia/commons/0/0f/Lee_Kuan_Yew.jpg");
CREATE TABLE listings (
id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
title VARCHAR(100) NOT NULL,
description_i VARCHAR(1000) NOT NULL,
price INT(6) NOT NULL,
fk_poster_id INT NOT NULL,
KEY fkPosterID (fk_poster_id),
CONSTRAINT FOREIGN KEY (fk_poster_id) REFERENCES users(id) ON DELETE NO ACTION ON UPDATE NO ACTION,
created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
) ENGINE=INNODB;
-- THESE ARE JUST EXAMPLES AND TEST KITS.TO BE REMOVED BEFORE PRESENTATION.
INSERT INTO listings (title, description_i, fk_poster_id, price) VALUES
("iPhone 6s USED","In good condition. Camera and screen not working.","2","250"),
("Samsung S7 NOT USED","In bad condition. Screen fully smashed. Can't even operate.","3","10000");
CREATE TABLE offers (
id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
fk_offeror_id INT NOT NULL,
KEY fkOfferID (fk_offeror_id),
CONSTRAINT FOREIGN KEY (fk_offeror_id) REFERENCES users(id) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=INNODB;
SELECT * FROM users;
SELECT * FROM listings;
My current controller codes
var express = require('express');
var app = express();
const userJs = require('../model/user')
const listingJs = require('../model/listing')
var bodyParser = require('body-parser');
var urlencodedParser = bodyParser.urlencoded({ extended: false });
app.use(bodyParser.json()); //parse appilcation/json data
app.use(urlencodedParser);
app.get("/users/:user_id/listings/",(req,res) => {
var user_id = req.params.id;
userJs.getListingsByUserID(user_id, (error,results) => {
if (error) {
res.status(500).send("Internal Server Error")
}
res.status(200).send(results);
});
})
And my current user.js codes
var db = require('./databaseConfig.js')
const users = {getListingsByUserID: function (user_id, callback) {
const getListingsByUserIDQuery = 'SELECT u.id,l.title,l.description_i,l.price,l.fk_poster_id,l.created_at FROM listings l INNER JOIN users u ON u.id = l.fk_poster_id WHERE u.id = ?;';
db.query(getListingsByUserIDQuery,[user_id],(error,results) => {
if (error) {
callback(error,null);
return;
};
callback(null,results);
})
}
module.exports = users;

Answer 1

Just try to use Promise instead of callback like this:
const users =
{
function getListingsByUserID(user_id)
{
return new Promise((resolve, reject) =>
{
db.query(getListingsByUserIDQuery,[user_id],(error,results) =>
{
if (error)
{
return reject(error);
}
else
{
return resolve(results);
}
});
});
});
};
If you want result through callback method then try callback(null,results[0]);