public function last_modified($translation_set)
{
global $wpdb;
$last_modified = wp_cache_get($translation_set->id, 'translation_set_last_modified');
// Cached as "" if no translations.
if ("" === $last_modified) {
return false;
} elseif (false !== $last_modified) {
return $last_modified;
}
$last_modified = $wpdb->get_var($wpdb->prepare("SELECT date_modified FROM {$this->table} WHERE translation_set_id = %d AND status = %s ORDER BY date_modified DESC LIMIT 1", $translation_set->id, 'current'));
wp_cache_set($translation_set->id, (string) $last_modified, 'translation_set_last_modified');
return $last_modified;
}