multiple queries in node js and mysql

Question

I am working on a project in node js using a mysql database. I want to perform queries in the index.j file. The code worked for two connections however when i add the third query I don't know what numbers to use inside results[][]. Can you please help? Thank you.

Here is the code in index.js file

router.get('/StudentPage', function (req, res, next) {
if (req.session && req.session.user) {
    pool.getConnection(function (err, connection) {

        async.parallel([
            function (callback) { connection.query('select * from students where Email = ' + connection.escape(req.session.user.Email), callback) },
            function (callback) { connection.query('select * from reservations where student_email = ' + connection.escape(req.session.user.Email), callback) },
            function (callback) { connection.query('select * from complaint where student_email = ' + connection.escape(req.session.user.Email), callback)}
        ], function (err, results) {
            if (!results[0][0]) {
                req.session.reset();
                res.redirect('/');
            } else {
                res.render('student', { title: 'Student Page', userinfo: results[0][0], reservations: results[1][0], complaints: results[2][0]});
            }
            connection.release();
        });
    });
} else {
    res.redirect('/');
}
});

YarGnawh · Accepted Answer · 2016-01-03 23:54:45Z

1

Try using a key value object instead of an array for async.parallel

// an example using an object instead of an array
async.parallel({
    one: function(callback){
        setTimeout(function(){
            callback(null, 1);
        }, 200);
    },
    two: function(callback){
        setTimeout(function(){
            callback(null, 2);
        }, 100);
    }
},
function(err, results) {
    // results is now equals to: {one: 1, two: 2}
});

For example:

router.get('/StudentPage', function (req, res, next) {
if (req.session && req.session.user) {
    pool.getConnection(function (err, connection) {

        async.parallel({
            students: function (callback) { 
                connection.query('select * from students where Email = ' + connection.escape(req.session.user.Email), callback) 
            },
            reservations: function (callback) { 
                connection.query('select * from reservations where student_email = ' + connection.escape(req.session.user.Email), callback) 
            },
            complaints: function (callback) { 
                connection.query('select * from complaint where student_email = ' + connection.escape(req.session.user.Email), callback)
            }
        }, function (err, results) {
            if (!results.students || !results.students[0]) {
                req.session.reset();
                res.redirect('/');
            } else {
                res.render('student', { 
                    title: 'Student Page', 
                    userinfo: results.students[0], 
                    reservations: results.reservations[0], 
                    complaints: results.complaints[0]
                });
            }
            connection.release();
        });
    });
} else {
    res.redirect('/');
}
});

edited Jan 3, 2016 at 23:54

answered Jan 3, 2016 at 23:19

YarGnawh

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4 Comments

Souraya Over a year ago

how would i use it in my case. I didn't understand the syntax so that i can use it. Do you mind explaining it? Thank you

Souraya Over a year ago

I tried it however i got a reference error saying that complaints is not defined

YarGnawh Over a year ago

double check your query and add check for empty array for each result (results.complaints.length > 0 ? results.complaints[0] : null)

Souraya Over a year ago

The query is right since i copied it into mysql server and it gave me the results in the table

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