the pause in execution before my function redirects to a different route

Question

the pause in execution before my function redirects to a different route

Currently, I am developing a page using nodeJs with express which is supposed to display a table. However, I encountered an issue with my variable "allMusique" that contains the data for my page. When trying to access it initially, there seems to be an error. But strangely, when I refresh the page once, everything shows up correctly with all the data displayed. Can anyone identify what might be the problem here?

Below is the snippet of my code:

var express = require('express');
var router = express.Router();
var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";
var allMusique;
var idMaxMusique;

router.get('/', function(req, res, next) {
    function getAllMusique(){
        MongoClient.connect(url, function(err, db) {
            if (err) throw err;
            var dbo = db.db("projet_node");
            dbo.collection("musiques").find({}).toArray(function(err, result) {
                if (err) throw err;
                allMusique = result;
                var size = allMusique.length-1;
                idMaxMusique = parseInt(result[size].id)+1;
            });
        });
    }

    getAllMusique();
    res.render('musiques', { resultat: allMusique, idMax: idMaxMusique });
});

module.exports = router;

javascript node.js express routes

Answer 1

Answer №1

When you first call res.render, the variable allMusique is not yet set because it did not wait for the database access to finish. On the second attempt, it is already populated due to the initial database access.

I suggest calling res.render inside the Mongoclient.connect function.

router.get('/', function(req, res, next) {
    MongoClient.connect(url, function(err, db) {
        if (err) throw err;
        var dbo = db.db("projet_node");
        dbo.collection("musiques").find({}).toArray(function(err, result) {
            if (err) throw err;
            allMusique = result;
            var size = allMusique.length-1;
            idMaxMusique=parseInt(result[size].id)+1; 
            res.render('musiques', { resultat: allMusique, idMax: idMaxMusique });
        });
    });
});

If you want to maintain the structure, you can convert the res.render into a function callback.

function getAllMusique(callbackFunction){
    MongoClient.connect(url, function(err, db) {
        if (err) throw err;
        var dbo = db.db("projet_node");
        dbo.collection("musiques").find({}).toArray(function(err, result) {
            if (err) throw err;
            allMusique = result;
            var size = allMusique.length-1;
            idMaxMusique = parseInt(result[size].id)+1;
            callbackFunction();
        });
    });
}

getAllMusique(()=>res.render('musiques', { resultat: allMusique, idMax: idMaxMusique }));

Alternatively, you can make the function return a promise once the data has been retrieved and set.

function getAllMusique(){
    return new Promise((resolve, reject) => {
        MongoClient.connect(url, function(err, db) {
            if (err) throw err;
            var dbo = db.db("projet_node");
            dbo.collection("musiques").find({}).toArray(function(err, result) {
                if (err) throw err;
                allMusique = result;
                var size = allMusique.length-1;
                idMaxMusique = parseInt(result[size].id)+1;
                resolve();
            });
        });
    });
}

getAllMusique().then(()=>res.render('musiques', { resultat: allMusique, idMax: idMaxMusique }));

Answer 2

When you first call res.render, the variable allMusique is not yet set because it did not wait for the database access to finish. On the second attempt, it is already populated due to the initial database access.

I suggest calling res.render inside the Mongoclient.connect function.

router.get('/', function(req, res, next) {
    MongoClient.connect(url, function(err, db) {
        if (err) throw err;
        var dbo = db.db("projet_node");
        dbo.collection("musiques").find({}).toArray(function(err, result) {
            if (err) throw err;
            allMusique = result;
            var size = allMusique.length-1;
            idMaxMusique=parseInt(result[size].id)+1; 
            res.render('musiques', { resultat: allMusique, idMax: idMaxMusique });
        });
    });
});

If you want to maintain the structure, you can convert the res.render into a function callback.

function getAllMusique(callbackFunction){
    MongoClient.connect(url, function(err, db) {
        if (err) throw err;
        var dbo = db.db("projet_node");
        dbo.collection("musiques").find({}).toArray(function(err, result) {
            if (err) throw err;
            allMusique = result;
            var size = allMusique.length-1;
            idMaxMusique = parseInt(result[size].id)+1;
            callbackFunction();
        });
    });
}

getAllMusique(()=>res.render('musiques', { resultat: allMusique, idMax: idMaxMusique }));

Alternatively, you can make the function return a promise once the data has been retrieved and set.

function getAllMusique(){
    return new Promise((resolve, reject) => {
        MongoClient.connect(url, function(err, db) {
            if (err) throw err;
            var dbo = db.db("projet_node");
            dbo.collection("musiques").find({}).toArray(function(err, result) {
                if (err) throw err;
                allMusique = result;
                var size = allMusique.length-1;
                idMaxMusique = parseInt(result[size].id)+1;
                resolve();
            });
        });
    });
}

getAllMusique().then(()=>res.render('musiques', { resultat: allMusique, idMax: idMaxMusique }));

Answer 3

Answer №2

retrieveAllSongs is a promise-based function. Simply shift the rendering process inside the callback for optimal performance.

Answer 4

retrieveAllSongs is a promise-based function. Simply shift the rendering process inside the callback for optimal performance.

Answer 5

Answer №3

Another approach to solving this issue involves using async/await.

router.get('/', async function(req, res, next) {

//...

await getAllMusique();
res.render('musiques', { resultat: allMusique, idMax: idMaxMusique });

}

It's worth noting that the callback in .get() is now marked as async, enabling you to use await with your function.

Answer 6

Another approach to solving this issue involves using async/await.

router.get('/', async function(req, res, next) {

//...

await getAllMusique();
res.render('musiques', { resultat: allMusique, idMax: idMaxMusique });

}

It's worth noting that the callback in .get() is now marked as async, enabling you to use await with your function.

the pause in execution before my function redirects to a different route

Answer №1

Answer №2

Answer №3

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