public function getPrimarykey($table=null) 
    {
        if ($table) {
            return $this->getDb()->getPrimaryKey($table);
        } else {
            if (!isset($this->options['primary_key'])) {
                $pk = $this->getDb()->getPrimaryKey($this->getTableName());
                $this->options['primary_key'] = $pk;
            }
            
            return $this->options['primary_key'];
        }
    }