private function plugin_query($controller, $format)
{
$tables = DB_PLUGINS . ', ' . DB_PLUGINS_LOOKUP;
//set variable value to retrieve plugin_id
$columns = DB_PLUGINS_LOOKUP . '.plugin_id';
$where = DB_PLUGINS_LOOKUP . '.plugin_id=' . DB_PLUGINS . '.plugin_id AND ' . DB_PLUGINS_LOOKUP . '.plugin_type=? AND ' . DB_PLUGINS_LOOKUP . '.content_type=?';
$fields = array($controller, $format);
//build query and return results
$db_results = BuildQuery::all_field_query($tables, $columns, $where, $fields);
self::$db_all_plugins = $db_results;
}