Even for a Database connection class, you are not supposed to use the singleton design pattern.

Languages such as Java, use a connection pool. A connection pool is an implementation of the pool design pattern that is already explained in this course.

In PHP that is not possible. The reason why is because once a PHP file has finished execution, then the state is destroyed. I am aware of mysql-pconnect, but I have never used it to tell you for sure if that fixes this problem.

Laravel uses the factory design pattern to CREATE a database connection.

Inside config/app.php you define all the service providers that your application requires to work properly, one of them is DatabaseServiceProvider

Illuminate\Database\DatabaseServiceProvider::class

Inside that class, there is a register() method go there and then take a look at the code inside this method registerConnectionServices() .

$this->app->singleton('db', function ($app) {
    return new DatabaseManager($app, $app['db.factory']);
});

It passes a factory to the DatabaseManager class.

Inside DatabaseManager you have a connection() method. That method calls this protected method makeConnection() . makeConnection() uses the factory design pattern to create a new connection.

A Database class is a very complex object.

You just have to remember that Singleton is bad. It has its place, but 99.9% of the times it should be avoided.

Frameworks are very complex. I have been working on my own PHP framework for some time now. I hope I can finish it this year and publish it on GitHub.