spl_autoload_register(function($class_name) {
require_once 'classes/'.$class_name.'.php';
});

class DB
{

private static $conn;

private static $DB_HOST = 'localhost';
private static $DB_NAME = 'test';
private static $DB_USER = 'root';
private static $DB_PASS = '';




private function __construct ()
{
    try {
        $this->conn = new PDO(
            'mysql:host=' . self::$DB_HOST . ';dbname=' . self::$DB_NAME,
            self::$DB_USER,
            self::$DB_PASS,
            [PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES 'utf8'"]
        );
        echo "Успешное соединение с базой данных!";

    } catch (PDOException $e) {
        echo "Возникла неизвестна ошибка";
        $now_date = new DateTime();
        file_put_contents('log', 'Возникла ошибка в файле ' . __FILE__ . ' в строке '
            . __LINE__ . PHP_EOL . 'Дата возникновения ошибки: ' . $now_date->format('d.m.Y H:i:s')
            . PHP_EOL . 'Текст ошибки [' . $e->getCode() . '] - ' . $e->getMessage() . PHP_EOL
            . str_repeat('-', 80) . PHP_EOL, FILE_APPEND);
        exit;
    }
}

private function __clone () {}
private function __wakeup () {}

public static function getInstance()
{
    if (self::$conn != null) {
        return self::$conn;
    }

    return new self;
}
}

$db = DB::getInstance();

$stmt = $conn->prepare("INSERT INTO students (name, last_name, bd)
VALUES (:name, :last_name, :bd)");
$stmt->bindParam(':name', $name);
$stmt->bindParam(':last_name', $last_name);
$stmt->bindParam(':bd', $bd);


$name = $_POST['name'];
$last_name = $_POST['last_name'];
$bd = $_POST['bd'];
$stmt->execute();
$conn=null;

class DB
{

private static $DB_HOST = 'localhost';
private static $DB_NAME = 'test';
private static $DB_USER = 'root';
private static $DB_PASS = '';


protected static $instance = null;

protected function __construct() {}
protected function __clone() {}

public static function instance()
{
    if (self::$instance === null) {
        $opt = array(
            PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
            PDO::ATTR_EMULATE_PREPARES => FALSE,
        );
    }
        try {
            self::$instance = new PDO(
                'mysql:host=' . self::$DB_HOST . ';dbname=' . self::$DB_NAME,
                self::$DB_USER,
                self::$DB_PASS,
                $opt
            );
            echo "Успешное соединение с базой данных!";

        } catch (PDOException $e) {
            echo "Возникла неизвестна ошибка";
            $now_date = new DateTime();
            file_put_contents('log', 'Возникла ошибка в файле ' . __FILE__ . ' в строке '
                . __LINE__ . PHP_EOL . 'Дата возникновения ошибки: ' . $now_date->format('d.m.Y H:i:s')
                . PHP_EOL . 'Текст ошибки [' . $e->getCode() . '] - ' . $e->getMessage() . PHP_EOL
                . str_repeat('-', 80) . PHP_EOL, FILE_APPEND);
            exit;
    }
}

public static function __callStatic($method, $args)
{
    return call_user_func_array(array(self::instance(), $method), $args);
}

public static function run($sql, $args = [])
{
    if (!$args)
    {
        return self::instance()->query($sql);
    }
    $stmt = self::instance()->prepare($sql);
    $stmt->execute($args);
    return $stmt;
    }

}

$stmt = DB::prepare("INSERT INTO pdowrapper VALUES (NULL, ?)");
foreach (['Sam','Bob','Joe'] as $name)
{
    $stmt->execute([$name]);
}