Connecting to a MySQL database with PDO - php

Question

Pre-emptive apology: This post contains basic questions.However, I have searched and I have not found an answer, if there is one...sorry.
I am following some youtube tutorials for making a basic ajax web chat, and in the tutorial the person is using MySQLi to connect to the DB. I want to create the same ajax chat application except I want to use PDO instead of MySQLi.
The person uses these two files:
config.php
<?php
define('DB_HOST', 'localhost');
define('DB_USER', 'bucky_chat');
define('DB_PASSWORD', '123456');
define('DB_NAME', 'bucky_chat');
?>`
chat.class.php
<?php
require_once('config.php');
require_once('error_handler.php');
class Chat {
private $mysqli;
//constructor opens DB connection
function __construct(){
$this->mysqli = new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME);
}
//destructor closes db connection
function __destruct(){
$this->mysqli->close();
}
}
?>
I'm trying to replicate the above snippets with PDO. The problem is that I'm not sure how to adapt the PDO examples I have looked at to do this.
First of all I'm confused as to why he defined these things in a separate file.. are there any benefits in doing this?
In another PDO tutorial I am looking at I see it can be done the followings way:
<?php
$config['db'] = array(
'host' => 'localhost',
'username' => '',
'password' => '',
'dbname' => ''
);
$db = new PDO('mysql:host=' . $config['db']['host'] . ';dbname=' . $config['db']['db_name'], $config['db']['username'], $config['db']['password']);
//some code
$db = null; //closes connection
?>
`
I think this is what I need to use (in a try catch block), but why does he put these things in an array? it seems to over complicate things... why not just variables? But does this code replicate the mysqli example? Howcome I don't see __construct() being used with PDO?
Some minor questions...
When creating a website with a user, is there a standard place to store DB connection?
Any book recommendations?
Sorry for all these questions, All help is strongly appreciated!

Answer 1

To answer your questions:
First of all I'm confused as to why he defined these things in a separate file
The authentication details are defined in a second file because if you create another query script, now both scripts can include the authentication details. If the authentication details change, you only need to update one file. If you are just writing a simple application, than just keep everything in one file.
but why does he put these things in an array
I think this is just done in-case the authentication details are needed someone else in the script (much like the defined globals from your first sample). Its often best practice to define parameters into variables (even if you use the variable once). This way, if you typo a variable, you will get an error; versus copy and pasting the same string over and over again.
Howcome I don't see __construct() being used with PDO
When ever you create a new object in PHP, you do not need to call __construct, it is called automatically with the "new" statement.
$PDOConnection = new PDO($dsn, $username, $password);
When creating a website with a user, is there a standard place to store DB connection
Definitely make sure the authentication details are stored in an inaccessible file to the public. The connection object has no harm to be accessed by the public (unless of course you need to authenticate the client (website user) before establishing a database connection). Is is best practice to always begin your (secure) PHP files with:
<?php
BUT... never end the file with "?>". If an extra character is inserted after the "?>" on accident, your web server could display your whole script to the world (of course your Apache, etc... would have to be configured wrong). Like I said... best practices.
Any book recommendations?
Googleing "php arcitechture best practices" may help.

Answer 2

You are confusing WAY TOO MUCH things that can be explained in one answer. you don't even know what to ask.
Please, don't take the art of programming as a some sort of cheap trick one can learn in 2 hours. To write a AJAX-based chat one need to learn for at least several months. To learn by understanding, not by copy-pasting. To learn step by step, going from variables to arrays, from arrays to functions, from functions to classes and so on - not by throwing all the code they find in one bowl and then asking on SO how to deal with all that. One cannot get to another step without having understand a previous one. And of course all these youtube tutorials are definitive pieces of useless rubbish.
some of your confusions are:
__construct() method actually has nothing to do with PDO. Nor with mysql. this is a Chat class method. And method which is all wrong. Chat class shouldn't create its own connection but use already created one.
This thing on variables vs. array vs. constants doesn't really matter. To have connection options in a separate file is a good thing but nonetheless you need to have a connection code in the separate file as well, to avoid writing connection code in the every file.
You should not use this code in a try catch block (unless you have an idea what to do in case of error, which I doubt you have).
Before starting for a chat, you have to learn smaller, simpler applications, like telephone book or the like, to learn basic database operations, from which you'll be later able to build ANY application, like any house can be built of bricks.
PDO basics you can get right here, in the tag wiki. But OOP basics is not that easy.

Answer 3

First the reason you define config in different file is so that you can just include that file instead of writing the database configuration anytime you want database access. It is preferred best practice.
you can do:
try
{
$PDOConnection = new PDO('mysql:host='.DB_HOST.';dbname='.DB_NAME.'', DB_USER, DB_PASS);
$PDOConnection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
//Do you stuffs
$PDOConnection = null;
}
catch(PDOException $e)
{
//Do something with error
}

Answer 4

Why not just do:
<?php
$hostname = 'host';
$dbname = 'dbname';
$username = 'uname';
$password = 'pw';
try {
$db = new PDO("mysql:host=$hostname;dbname=$dbname", $username, $password);
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}
catch (PDOException $ex) {
echo "An Error occurred!";
}
?>
In a separate PHP file I call mine dbPDO.php and then have:
require_once("dbPDO.php");
In your PHP pages. And then run queries by doing:
EDIT: to condense my answer.
$username = $_POST['username'];
$stmt = $db->prepare("SELECT field1, field2, field3, etc FROM mytable WHERE username = :username");
$stmt->bindParam(':username', $username);
$stmt->execute();
while ($r = $stmt->fetch()) {
$field1 = $r['field1'];
$etc = $r['etc'];
}
Make sure you bindParam and use the ':' in the query. Don't just put WHERE username = $username or WHERE username = $_POST['username'] That would led you prone to SQL Injection. Also, I didn't show it here, but you should have some sort of exemption handling for each query. I place the whole query in a Try/Catch, but I hear there are other ways to deal with it. I personally think its personal preference.

Answer 5

First of all you don't need an array nor variables, you can directly input the configuration..like:
try { //try connection
//common db
$db = new PDO('mysql:host=localhost;dbname=some_db_name', 'some_usernane', 'some_pass');
$db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (Exception $e) { //connection failed
die("Oh no! It seems we took too long to respond, we are sorry for that..");
}
Secondly _constructor() means that whenever the class Chat is called everything in the _constructor() is executed .
Here is a good tutorial for PDO http://wiki.hashphp.org/PDO_Tutorial_for_MySQL_Developers