How to select with parse.com in javascript

Question

How can I select in javascript ? I use parse.com as a database, this is my code, but it doesn't work

app.get('/students', function (req, res) {
    var students = Parse.Object.extend("students");
    var query = new Parse.Query(students);
    query.find({
        success: function (results) {
            for (var i = 0; i < results.length; i++) {
                var students = results[i];
                alert(students.get('Name')+ ' - ' + students.get('Lname')+ ' - ' + students.get('class_id'));
                    res.render('students/index', { students: students});
            }
        }
        })

And the logs error:

I2014-07-18T15:47:16.779Z] Error: cannot call http.ServerResponse.end() multiple times
at end (http.js:428:13)
at renderErrorResponse (connect_proto.js:155:15)
at next (connect_proto.js:187:9)
at fn (express_response.js:758:25)
at View.exports.renderFile [as engine] (jade.js:1149:5)
at View.render (express_view.js:77:8)
at Function.app.render (express_application.js:516:10)
at res.render (express_response.js:763:7)
at query.find.success (routes/students.js:28:29)
at Parse.js:2:5786

Could you help me please ?

Answer 1

As per the error message, you're calling something multiple times that you should only call once.

You shouldn't call res.render(..) inside a loop. The idea is to gather the data needed (inside a loop if needed) and then call the render() method at the end.

You are looping through the results (which is a collection of students rows), though your naming is confusing as you are using "students" to refer to a single student... anyway, from what I can understand of your intent you could simply do the following:

query.find({
    success: function (students) {
        res.render('students/index', students);
    }
});

NOTE: I named the results parameter fed to the success handler students instead, since it is an array of students.

Answer 2

Thank's, and I find how to select in parse.com with javascript

app.get('/students', function (req, res) {
    var students = Parse.Object.extend("students");
    var query = new Parse.Query(students);
    query.find({
        success: function (results) {
            //var students_data
            for (var i = 0; i < results.length; i++) {
                var object = results[i];
                console.log(object.id + ' - ' + object.get('Nom'));
            }
            res.render('students/index', { students: results });