Event-driven asynchronous callbacks in Node js - node.js

Question

Is there a way to block the asynchronous callback property of node.js?
Please Advice...
For example,
var express = require('express');
var app = express();
var MongoClient = require('mongodb').MongoClient,
format = require('util').format;
var cors = require('cors');
app.get('/gantt', cors(), function (request, response) {
MongoClient.connect('mongodb://127.0.0.1:27017/test', function (err, db) {
if (err) throw err;
var collection = db.collection('ganttdata');
collection.find({}, {
"_id": 0
}).toArray(function (err, results) {
var jsonString = JSON.stringify(results);
response.setHeader('Content-Type', 'text/plain');
response.send('{\"data\":' + jsonString + '}');
});
});
});
app.listen(3000);
console.log('Listening on port 3000...');
Inspite the Node.js prints the console statement first,i want app.get() to be executed.
My scenario is same as that of the above one.
This is my scenario
var ganttresult = new Array();
app.get('/get', cors(), function (request, response) {
console.log('hello');
connection.query("SELECT distinct id FROM ganttdata", function (err, rows) {
if (err) {
console.log('error in fetching ' + err);
} else {
var all_id = rows;
for (var j = 0; j < all_id.length; j++) {
console.log('hello1');
connection.query("SELECT id,tailName FROM ganttdata where id= '" + all_id[j].id + "'", function (err, rows) {
if (err) {
console.log('error in fetching ' + err);
} else {
var jsonString1 = rows;
var set_id = jsonString1[0].id;
connection.query("SELECT item_id,name,start,end FROM ganttdata where id= '" + set_id + "'", function (err, rows) {
if (err) {
console.log('error in fetching ' + err);
} else {
var jsonString2 = rows;
var gantt1 = new Object();
gantt1.id = jsonString1[0].id;
gantt1.tailName = jsonString1[0].tailName;
var series = new Array();
for (var i = 0; i < jsonString2.length; i++) {
var gantt2 = new Object();
gantt2.item = jsonString2[i];
series.push(gantt2);
gantt1.series = series;
}
//console.log(gantt1);
console.log('hi');
ganttresult.push(gantt1);
console.log(ganttresult);
}
});
}
});
}
var result = JSON.stringify(ganttresult);
console.log(result);
response.send('{\"data\":' + result + '}');
response.end();
}
});
});
When I run this code,
I get an empty resultset and when I re-run I get the result.
I guess it is due to asynchronous callback nature of node js.
Please advice...
Thanks
I have tried async.waterfall method as given below
app.get('/get',cors(), function(request,response) {
async.waterfall([
function(result) {
connection.query("SELECT id FROM Gantt",function(err, rows) {
if (err) {
console.log('error in fetching ' + err);
}
else{
var all_id=rows;
for(var j=0;j<all_id.length;j++){
connection.query("SELECT id,tailName FROM Gantt where id= '"+all_id[j].id+"'",function(err, rows) {
if (err) {
console.log('error in fetching ' + err);
}
else{
var jsonString1=rows;
var set_id=jsonString1[0].id;
connection.query("SELECT item_id,name,start,end FROM GanttFlight where id= '"+set_id+"'",function(err, rows) {
if (err) {
console.log('error in fetching ' + err);
}
else{
var jsonString2=rows;
var gantt1=new Object();
gantt1.id=jsonString1[0].id;
gantt1.name=jsonString1[0].tailName;
var series = new Array();
series=[];
for(var i=0;i<jsonString2.length;i++){
var gantt2=new Object();
gantt2.item=jsonString2[i];
series.push(gantt2);
gantt1.series=series;
}
ganttresult.push(gantt1);
}
});
}
});
}
var result= JSON.stringify(ganttresult);
console.log(ganttresult);
response.send(ganttresult);
ganttresult=[];
//response.send('{\"data\":'+result+'}');
response.end();
}
});
}
], function(err, status) {
console.log(status);
});
});
app.listen(3000);
console.log('Listening on port 3000...');
i am getting empty result first and when refresh the browser,i get the required result
Please Advice