validate 9 digit code before sending visitor on

// http://www.gravityhelp.com/forums/topic/database-look-up-validation
// validate 9 digit code
// change the 70 here to your form ID
add_filter('gform_validation_70', 'validate_code');
function validate_code($validation_result){
    // this assumes the code is entered in field one on your form
    // change this input_ number if it's a different field
    if(!is_code_valid($_POST['input_1'])){
        $validation_result['is_valid'] = false;
        foreach($validation_result['form']['fields'] as &$field){
        // field 1 is the field where we want to show the validation message
            if($field['id'] == 1){
                $field['failed_validation'] = true;
                $field['validation_message'] = 'The code you entered is invalid: please try again.';
                break;
            }
        }
    }
    return $validation_result;
}

// use this function to validate codes
function is_code_valid($thiscode){
    // read all the codes in from the numbers.txt file
    // change the path here to the location of your file
    $codes = file('/kunden/homepages/99/d12345678/htdocs/numbers.txt', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
    foreach($codes as $code){
        // compare the entered code to all codes in the file until we find a match
        if($thiscode == $code){
            return TRUE;
        }
    }
    // if we did not have a match and are out of codes, return FALSE
    return FALSE;
}

// doing this here because the redirect URL does not support variables or shortcodes
// change the 70 here to your form ID
add_filter('gform_confirmation_70', 'valid_invitation_confirmation', 10, 4);
function valid_invitation_confirmation($confirmation, $form, $lead, $ajax){
    // customize this URL - I send the code in the query string
    $success_url = get_bloginfo('url') . '/?code=' . $lead[1];
    $confirmation = array('redirect' => $success_url);
    return $confirmation;
}