public function tableExists($table_name,$which_connection='')
    {
        /**
          Check whether the definition is in cache
        */
        if (isset($this->structure_cache[$which_connection]) && isset($this->structure_cache[$which_connection][$table_name])) {
            return true;
        }

        $conn = $this->getNamedConnection($which_connection);
        if (!is_object($conn)) {
            return false;
        }
        $cols = $conn->MetaColumns($table_name);
        if ($cols === false) {
            return false;
        }

        return true;
    }