Undefined push to array - Basic Application using ExpressJs and 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
    });
});