public function get($id, $ignore_cache = false){
        if( empty($this->primary_key) ){
            return null;
        }
        $row = $this->where("{$this->table}.{$this->primary_key} = %d", $id)->get_row('', $ignore_cache);
        if( $row && $this->result_class ){
            return new $this->result_class($row);
        }else{
            return $row;
        }
    }