function delete(){
        if($this->notORM->freeze){
            return false;
        }
        //防止误删，禁止全表的删除
        //@dogstar - 2014-10-24
        $where = $this->whereString();
        if(empty($where)){
            throw new Exception('sorry, you can not delete the whole table --dogstar');
        }

        $return = $this->query("DELETE" . $this->topString($this->limit) . " FROM $this->table" . $where, $this->parameters);
        if(!$return){
            return false;
        }
        return $return->rowCount();
    }