php singleton database connection, is this code bad practice?
Solution 1
Singletons are bad news.
- They introduce global state into a program. Most programmers should be familiar with why global state is bad.
- They introduce tight coupling between the singleton and any class that uses it. This means you can't reuse the classes in question without reusing the singleton too.
- They make unit testing of classes that depend on the singleton problematic because you can't easily replace the singleton with a mock.
- They encourage a coding style where classes attempt to resolve their own dependencies. This is bad because it can reduce clarity regarding what dependencies the class has.
- PHP has a Share Nothing Architecture, meaning that PHP singletons aren't really singletons at all, there can be multiple instances alive at any one time (one per open request).
- What happens if you suddenly discover at some later date that you actually need more than one of the resource that's being provided by the singleton? It's a more common scenario than you might think
You're better off looking at dependency-injection instead, as it resolves the above issues.
Solution 2
I think a singleton can be OK for a connection manager, but not for a connexion itself.
You never know when you'll need to have an extra connection for a specific part of your development. Let say you suddently need to add a synchronisation with a remote database.
A connection manager (who can manage multiple connection) can be a singleton. A connection itself; no.
You connection manager should also be able to load "Drivers", so that you'll be able to instanciate a MySQL connection and the day you need msSQL, sqLite or anything else, you're able to add the needed drivers.
matt
Updated on June 04, 2022Comments
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matt almost 2 years
I'm trying to create a simple to use singleton class to connect to mysql database and do queries, the code works fine and i haven't had any problems with it, but since I'm new to OOP I'm wondering whether this is bad practice or not.
Here's the class
class Database { private $databaseName = 'dbname'; private $host = 'localhost'; private $user = 'user'; private $password = 'pass'; private static $instance; //store the single instance of the database private function __construct(){ //This will load only once regardless of how many times the class is called $connection = mysql_connect($this->host, $this->user, $this->password) or die (mysql_error()); $db = mysql_select_db($this->databaseName, $connection) or die(mysql_error()); echo 'DB initiated<br>'; } //this function makes sure there's only 1 instance of the Database class public static function getInstance(){ if(!self::$instance){ self::$instance = new Database(); } return self::$instance; } public function connect() { //db connection } public function query($query) { //queries $sql = mysql_query($query) or die(mysql_error()); return $sql; } public function numrows($query) { //count number of rows $sql = $this->query($query); return mysql_num_rows($sql); } } //Intantiate the class $database = Database::getInstance();
and when i want to use the class I would do:
$query = "SELECT * FROM registrations"; echo $database->numrows($query); $sql = $database->query($query);