Global Variable - database connection?

Question

I am trying to connect to a database (MySQLi) just once, but am having problems doing so.

How do I make a connection global for the entire script? There are multiple files (index.php, /classes/config.class.php, /classes/admin.class.php, etc).

I've tried the following:

In: config.class.php

public static $config = array();
public static $sql;

function __construct() {
    // database
    db::$config['host'] = 'localhost';
    db::$config['user'] = '_';
    db::$config['pass'] = '_';
    db::$config['db'] = '_';

    // connect
    db::$sql = new mysqli(db::$config['host'], db::$config['user'], db::$config['pass'], db::$config['db']);
}

Again, in config.class.php

public function contectToDatabase($sql){
    $sql = new mysqli(db::$config['host'], db::$config['user'], db::$config['pass'], db::$config['db']);
    $this->sql = $sql;
}

I use the class with the following code: $config = new db();

I really am puzzled at how I'm to do this. Can anyone help?

--- Edit --- This is my new config.class.php file:

public static $config = array();
public static $sql;

private static $db;
private $connection;

public function __construct() {
    // database
    db::$config['host'] = '_';
    db::$config['user'] = '_';
    db::$config['pass'] = '_';
    db::$config['db'] = '_';
    // connect
    $this->connection = new mysqli(db::$config['host'], db::$config['user'], db::$config['pass'], db::$config['db']);
}
function __destruct() {
    $this->connection->close();
}
public static function getConnection() {
    if($db == null){
        $db = new db();
    }
    return $db->connection;
}

And this is how I'm loading it:

require_once("classes/config.class.php");
$config = new db();
$sql = db::getConnection();

However, running a real_escape_string results in the following errors:

Warning: mysqli::real_escape_string() [mysqli.real-escape-string]: Couldn't fetch mysqli in /home/calico/_/_.com/_/index.php on line 20

Warning: mysqli::query() [mysqli.query]: Couldn't fetch mysqli in /home/calico/_/_.com/_/index.php on line 28

or you could learn Dependency Injection instead of using the singleton antipattern — Gordon
– Gordon, Commented Oct 17, 2011 at 11:26
Yeah… singletons always result in hot debates. I was just giving input and ideas — knittl
– knittl, Commented Oct 17, 2011 at 11:28
Is there any way to have the connection as a global variable for each class? Eg: I set up a global variable called $sql, and set it to $sql = new mysqli(db::$config['host'], db::$config['user'], db::$config['pass'], db::$config['db']);? I don't want to repeat the database connectoin for every class. — Peter
– Peter, Commented Oct 17, 2011 at 12:16

Reed · Accepted Answer · 2015-09-15 15:55:54Z

17

Personally, I use a singleton class. Something like this:

<?php

class Database {

    private static $db;
    private $connection;

    private function __construct() {
        $this->connection = new MySQLi(/* credentials */);
    }

    function __destruct() {
        $this->connection->close();
    }

    public static function getConnection() {
        if (self::$db == null) {
            self::$db = new Database();
        }
        return self::$db->connection;
    }
}

?>

Then just use $db = Database::getConnection(); wherever I need it.

edited Sep 15, 2015 at 15:55

Reed

15k8 gold badges74 silver badges114 bronze badges

answered Oct 17, 2011 at 11:24

daiscog

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6 Comments

Gordon Over a year ago

Your Singleton can be serialized and cloned which means it does not ensure there is only one instance.

Peter Over a year ago

OK, I've added it to the config class, and have attempted to load it. However, there are errors (see the main post, under the ---edit--- line). Any ideas whats wrong?

daiscog Over a year ago

@Peter Don't add it to another class. This is a singleton class that should be stand-alone and should not have a public constructor. Just use $db = Database::getConnection(); to get an open MySQLi instance wherever you need it.

daiscog Over a year ago

@Gordon Yes, this is just a quick example; hence "Something like this"

AGDEV Over a year ago

Could I implement PDO with this?

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