Patrón MVC básico

Controller.php

protected function getSql($key)
{
    if (isset($_POST[$key]) && !empty($_POST[$key])) {
        $_POST[$key] = strip_tags($_POST[$key]);

        if (!get_magic_quotes_gpc()) {
            $mysqli = new mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME);
            if ($mysqli->connect_error) {
                die('Connection error (' . $mysqli->connect_errno . ') '
                    . $mysqli->connect_error);
            } else {
                $_POST[$key] = $mysqli->real_escape_string($_POST[$key]);
            }

        }

        return trim($_POST[$key]);
    }
}