settings.php

//src/settings.php
<?php

return [
    'db' => [
        'host' => 'localhost',
        'dbname' => 'my_project',
        'user' => 'root',
        'password' => '',
    ]
];

Db.php

//src/MyProject/Services/Db.php
<?php

namespace MyProject\Services;

class Db
{
    private static $instance;

    /** @var \PDO */
    private $pdo;

    private function __construct()
    {
        $dbOptions = (require __DIR__ . '/../../settings.php')['db'];

        $this->pdo = new \PDO(
            'mysql:host=' . $dbOptions['host'] . ';dbname=' . $dbOptions['dbname'],
            $dbOptions['user'],
            $dbOptions['password']
        );
        $this->pdo->exec('SET NAMES UTF8');
    }

    public function query(string $sql, array $params = [], string $className = 'stdClass'): ?array
    {
        $sth = $this->pdo->prepare($sql);
        $result = $sth->execute($params);

        if (false === $result) {
            return null;
        }

        return $sth->fetchAll(\PDO::FETCH_CLASS, $className);
    }

    public static function getInstance(): self
    {
        if (self::$instance === null) {
            self::$instance = new self();
        }

        return self::$instance;
    }
}

вызов

Db::getInstance()
return $db->query('SELECT * FROM `articles`;', [], Article::class);