Undefined push to array - Basic Application using ExpressJs and MySQL - mysql

Question

First of all, I have to tell you I'm pretty noob in this "universe". I'm using: ExpressJs, MySql, Body-Parser, Express-session, Ejs template for creating an Basic Contacts Application in Node.
My database is composed from 3 tables:
user (user_id, first, second name, username, password)
contacts (ct_id, first, second name, phone numb.)
user_contacts (user_id, ct_id) --> foreign keys for user and contacts
I want to listing on /myProfile page all details about user and his contacts.
I don't know how to handle the select queries.
So, after some documentation I did this:
conn.query('SELECT * FROM user_contacts WHERE user_id= ?', req.session.user_id, function (err, result) {
if(err) throw err;
console.log(result);
var queryArray = "";
for(var i = 0; i < result.length; i++){
queryArray += `SELECT * FROM contacts WHERE ct_id= ${result[i].ct_id}; `;
}
console.log(queryArray);
conn.query(queryArray, function (err, result) {
if(err) throw err;
console.log(result);
res.render('myProfile/contacts', {
title: `${req.session.user_nickname}'s Contacts`,
data: result
});
});
});
But I have an error
ER_PARSE_ERROR: You have an error in your SQL syntax;
..when queryArray.length > 1
I searched and it's something about Multiple statement queries but I dont know how to solve it.
Edit 2:
I modify my code..
conn.query('SELECT * FROM user_contacts WHERE user_id= ?', req.session.user_id, function (err, result) {
if(err) throw err;
var datas = [];
for(var i = 0; i < result.length; i++){
getContacts = function(query){
conn.query(query, function (err, result) {
console.log('Creating data');
data = {
user: req.session.user_nickname,
contact:{
ct_firstName: result[0].ct_firstName,
ct_SecondName: result[0].ct_SecondName,
ct_PhoneNumber: result[0].ct_PhoneNumber
}
}
return data;
});
}
console.log('Send data to array');
datas.push(getContacts(`SELECT * FROM contacts WHERE ct_id = ${result[i].ct_id}`));
}
console.log(datas); // [ undefined, undefined ]
res.render('myProfile/contacts',{
title: `${req.session.user_nickname}'s profile`,
data: datas
})
});
But now my array contain undefined objects?? Any solution?
Maybe is something about scope?
My result:
Send data to array
Send data to array
[ undefined, undefined ]
Creating data
Creating data
I push the object to array before creating it. How is it possible?

Answer 1

1797,
I noticed you have several small queries grabbing the contact info for a given user. You could simplify your code by combining your queries into a single one. Often times 1 big query is more efficient (plus it's easier to maintain). I'm using a join. More info here.
const contacts = [];
const query = "
SELECT c.*
FROM user_contact uc
JOIN contact c ON uc.contact_id = c.contact_id
WHERE uc.user_id = ?
GROUP BY c.contact_id
";
conn.query(query, req.session.user_id, (err, results) => {
if (err) throw new Error(err);
// it seems that this could just be 'contacts = results' since they
// have the same structure
contacts = results.map(result => {
return {
ct_firstName: result[0].ct_firstName,
ct_SecondName: result[0].ct_SecondName,
ct_PhoneNumber: result[0].ct_PhoneNumber
};
});
res.render('myProfile/contacts',{
title: `${req.session.user_nickname}'s profile`,
data: contacts
});
});