Initializing connection to a MySQL database in PHP

I wanted to get some feedback on this way of initializing a connection to a MySQL database.

File includes/db.php:

<?php
$config_path = __DIR__ .  '/../config/database.ini';

$db_ini = parse_ini_file($config_path , true);
$db_info['db_host'] = $db_ini['db_data_source_name']['host'];
$db_info['db_user'] = $db_ini['db_general']['user'];
$db_info['db_pass'] = $db_ini['db_general']['password'];
$db_info['db_name'] = $db_ini['db_data_source_name']['dbname'];

foreach($db_info as $key => $value) {
    $upper_key = strtoupper($key);
    if (!defined($upper_key)) {
        define($upper_key, $value);
    }
}

$connection = mysqli_connect(DB_HOST, DB_USER, DB_PASS, DB_NAME);

?>

Is there anything wrong with the file above being included in other php files as needed?

Thank you!

Scope

The only real problem I can forsee is that you may end up re-initializing a new connection to the DB if you include this more than once. That’s an easy fix:

if(empty($connection)) $connection = ...

That way you will only re-init the connection if it hasn’t been created.

I personally prefer to keep things out of the global scope, so I often use a pattern like this:

class DB{
    private static $conn;
    public static getConn(){
        if(empty(self::$conn)){
            self::$conn = new mysqli(...);
        }
        return self::$conn;
    }
}

Then you can use DB::getConn() to get the DB connection and it will only create the connection once, and you don’t have to worry about accidentally naming a different variable $connection.

Maybe wrap that in a if(!class_exists("DB")){...} if you think you might include it more than once.

Efficiency

You are creating constants for your DB values. Essentially storing that data in memory even though you should only need it once. Because of this you also have to check if those constants exist before doing it again. This is an unnecessary check if you just use the values from the array instead of committing them to constants.

Why the intermediate step of writing values to array? Why not:

define('DB_HOST', $db_ini['db_data_source_name']['host']);
define('DB_USER', $db_ini['db_general']['user']);
// etc.

Be careful with relative path with regards to including in other pieces of code. If being included by code in another directory (particularly at a different level in directory structure), this may break. Also, you won’t be able to include this file more than once within any given script execution since you are defining constants.

Since you can only include this once per execution, do you really need to define constants at all?

$connection = mysqli_connect(
    $db_ini['db_data_source_name']['host'],
    $db_ini['db_general']['user'],
    $db_ini['db_general']['password'],
    $db_ini['db_data_source_name']['dbname']
);

I am just generally worried about your thinking of including this within other files “as needed”. That tends to make me think that you don’t have a good strategy around managing your application dependencies (such as database connection). Just sprinkling includes/requires throughout your code can really make your code fragile and hard to maintain. If you really want to take you application coding to another level, I would suggest familiarizing yourself with dependency injection, both in a philosophical sense as well as from a practical standpoint looking at typical PHP libraries that do this (Pimple, PHP-DI, or pretty much any popular framework has some level of dependency injection strategy).

Hopefully your ini file is separate from your codebase (i.e. not under revision control) to where you are storing your DB passwords in your code. If that is the case, consider taking the next step and have the ini file parsed in a different process such that this particular code is not responsible for reading configuration data from files that should perhaps should just be available in environmental variables.

With this code, you effectively have no idea which credentials are used to create a connection.

So, after Mike Brant I would suggest to make this code less bloated and more explicit

<?php
$config_path = __DIR__ .  '/../config/database.ini';
$db_ini = parse_ini_file($config_path , true);

$connection = mysqli_connect(
    $db_ini['db_data_source_name']['host'],
    $db_ini['db_general']['user'],
    $db_ini['db_general']['password'],
    $db_ini['db_data_source_name']['dbname']
);

while some constants defined elsewhere should be discarded.