How to make a database connection using the Singleton design standard

Question

Well I do many web applications, where I all use database, and every time I do a new project, I create a file responsible for making queries with the database (CRUD).

Only that I want to change this, I want to make a file where I have all these queries with the database, and I wanted to use the standard Singleton projects.

And I wanted a little help on how to put this file together.

Answer 1

The Pattern Singleton consists of always returning the same instance of a given class to any point in the application.

This is done by limiting the access to the constructor method and returning the instance through a static method, i.e., a method you can call without instantiating the class.

Follows a rapid implementation:

class BancoDeDados
{
    // Instância da classe
    private static $instance = null;
    private $conn;

    // Construtor privado: só a própria classe pode invocá-lo
    private function __construct()
    {
        $host = "localhost";
        $user = "root";
        $pswd = "root";
        $db = "banco";

        try {
            $this->conn = mysqli_connect($host, $user, $pswd, $db);
            $this->conn->set_charset('utf8');
        } catch (Exception $e) {
            die("Erro na conexão com MySQL! " . $e->getMessage());
        }
    }

    // método estático
    static function getInstance()
    {
        // Já existe uma instância?
        if (self::$instance == NULL)
            self::$instance = new BancoDeDados();   // Não existe, cria a instância 
        return self::$instance;                     // Já existe, simplesmente retorna
    }

    // Previne o uso de clone
    private function __clone() {}
}

// Usando a classe
$db = BancoDeDados::getInstance();

// Você não poderá fazer isso por causa do construtor privado:
$db = new BancoDeDados();

From there, develop methods for access to your bank class.

Answer 2

Singleton

Intent:

Ensure a single instance and provide a global access point throughout the application’s use cycle

First, Singleton is not for database use. If you need to use multiple databases, what happens? Singleton becomes a problem. If you need a pattern for database, look for DAO (for example). And if you don’t use it yet, try to work with PDO in the PHP, because it is much safer, flexible and meets well.

Second, Singleton in the PHP is unfeasible. The reason? To each request http made the PHP automatically destroys all instances. Whatever language or technology is used, any situation where the answer destroys the instance singleton makes no sense, because a new instance is generated at each request.

When using a pattern you need to understand well what problem it proposes to solve, if it fits in the resolution of your problem and if the environment in which you will apply it will allow that purpose to be fulfilled. Anything other than this you should avoid using, because instead of solving your problem it will end up creating many others.