public function prepare($bindings= array (), $byValue= true, $cacheFlag= null) {
        $this->stmt= null;
        if ($this->construct() && $this->stmt= $this->xpdo->prepare($this->sql)) {
            $this->bind($bindings, $byValue, $cacheFlag);
        } else {
            $this->xpdo->log(xPDO::LOG_LEVEL_ERROR, 'Could not construct or prepare query because it is invalid or could not connect: ' . $this->sql);
        }
        return $this->stmt;
    }