protected function in($field, array $values, $not=FALSE){
        $this->where.= $field . ' ';
        if($not){$this->where.= 'NOT ';}
        $this->where.= 'IN (';
        foreach ($values as $value) {
            $this->where.= "'$value',";
        }
        $this->where= rtrim($this->where, ',');
        $this->where.= ') ';
    }