ThomasK ThomasK - 2 years ago 120
SQL Question

How to properly set up a PDO connection

From time to time I see questions regarding connecting to database.

Most answers is not the way I do it, or I might just not get the answers correctly. Anyway; I've never thought about it because the way I do it works for me.

But here's a crazy thought; Maybe I'm doing this all wrong, and if that's the case; I would really like to know how to properly connect to a MySQL database using PHP and PDO and make it easy accessible.

Here's how I'm doing it:

First off, here's my file structure (stripped down):


* index.php

* initialize/
-- load.initialize.php
-- configure.php
-- sessions.php


At the very top, I have


# site configurations
# connect to database
require('root/somewhere/connect.php'); // this file is placed outside of public_html for better security.
# include classes
foreach (glob('assets/classes/*.class.php') as $class_filename){
# include functions
foreach (glob('assets/functions/*.func.php') as $func_filename){
# handle sessions

I know there's a better, or more correct, way to include classes, but can't remember what it was. Haven't gotten the time to look into it yet, but I think it was something with
. something like that...


Here I basically just override some php.ini-properties and do some other global configuration for the site


I've put the connection onto a class so other classes can extends this one...

class connect_pdo
protected $dbh;

public function __construct()
try {
$db_host = ' '; // hostname
$db_name = ' '; // databasename
$db_user = ' '; // username
$user_pw = ' '; // password

$con = new PDO('mysql:host='.$db_host.'; dbname='.$db_name, $db_user, $user_pw);
$con->exec("SET CHARACTER SET utf8"); // return all sql requests as UTF-8
catch (PDOException $err) {
echo "harmless error message if the connection fails";
$err->getMessage() . "<br/>";
file_put_contents('PDOErrors.txt',$err, FILE_APPEND); // write some details to an error-log outside public_html
die(); // terminate connection

public function dbh()
return $this->dbh;
# put database handler into a var for easier access
$con = new connect_pdo();
$con = $con->dbh();

Here I do believe there's room for massive improvement since I recently started learning OOP, and using PDO instead of mysql.

So I've just followed a couple of beginners tutorials and tried out different stuff...


Beside handling regular sessions, I also initialize some classes into a session like this:

if (!isset($_SESSION['sqlQuery'])){
$_SESSION['sqlQuery'] = new sqlQuery();

This way this class is available all over the place. This might not be good practice(?)...

Anyway, this is what this approach allows me to do from everywhere:

echo $_SESSION['sqlQuery']->getAreaName('county',9); // outputs: Aust-Agder (the county name with that id in the database)

Inside my
-class, which
-class, I have a public function called
which handles the request to my database.

Pretty neat I think.

Works like a charm

So that's basically how I'm doing it.

Also, whenever I need to fetch something from my DB from not within a class, I just do something similar to this:

$id = 123;

$sql = 'SELECT whatever FROM MyTable WHERE id = :id';
$qry = $con->prepare($sql);
$qry -> bindParam(':id', $id, PDO::PARAM_INT);
$qry -> execute();
$get = $qry->fetch(PDO::FETCH_ASSOC);

Since I put the connection into a variable inside connect_pdo.php, I just have referring to it and I'm good to go. It works. I get my expected results...

But regardless of that; I would really appreciate if you guys could tell me if I'm way off here. What I should do instead, areas I could or should change for improvement etc...

I'm eager to learn...

Answer Source

The goal

As I see it, your aim in this case is twofold:

  • create and maintain a single/reusable connection per database
  • make sure that the connection has been set up properly


I would recommend to use both anonymous function and factory pattern for dealing with PDO connection. The use of it would looks like this :

$provider = function()
    $instance = new PDO('mysql:......;charset=utf8', 'username', 'password');
    $instance->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $instance->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
    return $instance;

$factory = new StructureFactory( $provider );

Then in a different file or lower in the same file:

$something = $factory->create('Something');
$foobar = $factory->create('Foobar');

The factory itself should look something like this:

class StructureFactory
    protected $provider = null;
    protected $connection = null;

    public function __construct( callable $provider )
        $this->provider = $provider;

    public function create( $name)
        if ( $this->connection === null )
            $this->connection = call_user_func( $this->provider );
        return new $name( $this->connection );


This way would let you have a centralized structure, which makes sure that connection is created only when required. It also would make the process of unit-testing and maintenance much easier.

The provider in this case would be found somewhere at the bootstrap stage. This approach would also give a clear location where to define the configuration, that you use for connecting to the DB.

Keep in mind that this is an extremely simplified example. You also might benefit from watching two following videos:

Also, I would strongly recommend reading a proper tutorial about use of PDO (there are a log of bad tutorial online).

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