public function prepare($bindings= array (), $byValue= true, $cacheFlag= null) {
        if ($this->stmt === null || !is_object($this->stmt)) {
            if (!empty ($this->sql) && $stmt= $this->xpdo->prepare($this->sql)) {
                $this->stmt= & $stmt;
                $this->bind($bindings, $byValue, $cacheFlag);
            }
        }
        return $this->stmt;
    }