No hint of errors when trying to connect to a database - mysql

Question

I've been struggling to get MySQL working with node for a while. When I run the following code no errors are thrown, but simultaneously none of the console messages are being printed (except for the obvious one).
var app = require('express')();
var http = require('http').Server(app);
var mysql = require('mysql');
var connection = mysql.createConnection({
host : 'localhost',
user : 'root',
password : '******',
database : 'blogDB'
});
connection.connect(function(err) {
if(err) {
console.log('error when connecting to database:', err);
}
console.log('Connected to the database');
});
var queryString = 'SELECT * FROM blogs';
connection.query(queryString, function(err, rows, fields) {
if (err) throw err;
for (var i in rows) {
console.log('Post: ', rows[i].id);
}
});
connection.end();
http.listen(3306, function(){
console.log('listening on *:3306');
});
Output:listening on *:3306
On top of this, when I go to "localhost:3306" in the browser, a download is immediately started and nothing appears on the web page. The download is a file with no extensions, but contained the following:
J
5.6.19 tscvKP3M ÿ÷ € g?F!q6X:Y2*z mysql_native_password ! ÿ„#08S01Got packets out of order
I am not sure if that is relevant, but it certainly was not happening when I was not running MySQL. I have no idea how to troubleshoot this. Any ideas what could be going wrong?

Answer 1

The error here is you're coding node.js as if it were procedural. It's not.
connection.connect(function(err) {
if(err) {
console.log('error when connecting to database:', err);
}
console.log('Connected to the database');
var queryString = 'SELECT * FROM blogs';
//change from connection to "this" because you're inside the context of the connection object now
this.query(queryString, function(err, rows, fields) {
if (err) throw err;
for (var i in rows) {
console.log('Post Titles: ', rows[i].id);
}
});
});
Node.js uses a series of callbacks that run when a task is completed. So when you want to do something AFTER you're connected to the DB, you run that code inside the callback.
What your code is doing is attempting to connect to the database, then while attempting to connect to the database you're querying a database you're not connected to, and so on and so forth.
For sake of illustrating the principle a little more, node functions use the following general methodology.
//1
myObj.myFunc( function( err , foo , bar ) {
//A
});
//2
myObj.myOtherFunc( function( err , someVar ) {
//B
});
1 will always run before 2. A and B may run in either order depending on when 1 and 2 finish executing. A will always run after 1 is done. B will always run after 2 is done.
Hopefully that helps clear things up ;)

Answer 2

As it turns out, MySQL and the app were running using the same port (3306). Changing the app's port to 3307 did the trick.