alexanderhofstaetter

// Redirect to the query URL if the URL matches the regex
function cfqar_register_rewrite_rule()
{
    add_rewrite_rule('^(([0-9]{1,2})([a-z]|[A-Z])([0-9]))/?$', 'index.php?qr=$matches[1]', 'top');
}
add_action( 'init', 'cfqar_register_rewrite_rule' );

alexanderhofstaetter

// Try to get the post with the queried custom field value and do the actual redirect (or throw an 404)
function cfqar_redirect()
{
    if( get_query_var( 'qr' ) )
    {
        $posts = get_posts([
            'post_type'			=> 'product',
            'meta_key'			=> 'qr-code',
            'meta_value'		=>  get_query_var( 'qr' )
        ]); 

alexanderhofstaetter

// Add custom query variable
function cfqar_register_query_var( $vars )
{
    $vars[] = 'qr';
    return $vars;
}
add_filter( 'query_vars', 'cfqar_register_query_var' );