nodejs mysql variable access after promise - mysql

Question

I'm beginner into nodeJS world and i try to connect a mysql database. I first select a team (equipe) and after that i have to select all the members of this team.
Finally, i want to construct an array with my teams and the members (in the lesEquipes var). When the code comes to the 3rd then, my var is null ! WHY please ?
Here is my code :
class Database {
constructor() {
this.connection = mysql.createConnection({
host: "192.x.x.x",
user: "john",
password: "mypass",
database: "mybase"
});
}
query(sql, args) {
return new Promise((resolve, reject) => {
this.connection.query(sql, args, (err, result, fields) => {
if (err) return reject(err);
resolve (result);
});
});
}
close() {
return new Promise((resolve, reject) => {
this.connection.end(err => {
if (err) return reject (err);
resolve();
});
});
}
}
var database = new Database();
.............
app.post('/visu',function(req,res){
//console.log(nodedump(req.params.mdp));
//console.log(req.body);
// codage en dur de l'authentification
if((req.body.email == "john#gmail.com") && (req.body.mdp == "password")){
var leUser = "administrateur";
let lesEquipes = new Array();
let test = 'Toto';
database.query("select * from equipe order by id")
.then( result => {
for (var i = 0; i < result.length; i++) {
let courante = new Array();
let nomEquipe = result[i].nomEquipe;
let idEquipe = result[i].id;
courante[0] = result[i];
var sql2 = "select * from participant where equipe = " + result[i].id;
//console.log(sql2);
database.query(sql2)
.then(result2 => {
console.log("Membres de l'équipe : " + nomEquipe);
courante[1] = result2;
console.log("COURANTE 2 "+ JSON.stringify(courante));
lesEquipes[idEquipe] = courante;
let test = 'AUTRE CHOSE';
/*
console.log("QUERY 2 "+ JSON.stringify(result2));
for (var j = 0; j < result2.length; j++) {
participant = result2[j].nom;
console.log(participant);
}
*/
//res.render('visuEquipes.ejs', { user:leUser, equipes:lesEquipes});
//console.log("Contenu "+ JSON.stringify(lesEquipes));
return ""; //database.query(sql3);
});
}
console.log("Contenu "+ JSON.stringify(test));
console.log("Contenu "+ JSON.stringify(lesEquipes));
}).then(result3 =>{
console.log("result 3 : "+result3);
console.log("Contenu "+ JSON.stringify(test));
**// THIS VAR IS NULL NULL NULL lesEquipes
console.log("Contenu "+ JSON.stringify(lesEquipes));**
res.render('visuEquipes.ejs', { user:leUser, equipes : lesEquipes});
}).catch((err) => {
console.log(err);
database.close();
});

Answer 1

The problem is that you are executing asynchronous code inside a loop.
for (var i = 0; i < result.length; i++) {
/**/
database.query(sql2).then(result2 => {
/**/
});
}
So in .then(result3 =>{ the variable lesEquipes is very likely to have not been initialized.
You have to wait for all the promises to resolve. You can easly add an array of promises.
const promises = [];
for (var i = 0; i < result.length; i++) {
promises.push(database.query(sql2).then(result2 => {/*...*/}));
}
return Promise.all(promises);
Or you can use async-p library to iterate the array, or better you can use ES7 async-await constructs.