mysqli class (no transaction precompilation)

<?php
/**
 * Created by PhpStorm.
 * User: Administrator
 * Date: 2015/3/10
 * Time: 23:16
 */

class DB{
    #定义变量
    private  $host;
    private  $user;
    private  $password;
    private  $charset;
    private  $dbname;
    private  $mysqli;        #mysqlid 连接

    #定义构造函数
    /**
     * @param array $arr
     */
    public function  __construct($arr=array()){
        $this->host=isset($arr['host'])?$arr['host']:'localhost';
        $this->user=isset($arr['$password'])?$arr['user']:'root';
        $this->password=isset($arr['password'])?$arr['password']:'759114';
        $this->charset=isset($arr['charset'])?$arr['charset']:'utf8';
        $this->dbname=isset($arr['dbname'])?$arr['dbname']:'project';

        $this->mysqli= new mysqli($this->host,$this->user,$this->password,$this->dbname);

    }


    #对sql语句进行判断
    private function  exec($sql){
        if(!($this->mysqli->query($sql))){
            die($this->mysqli->error);                     #错误处理
        }
        return $this->mysqli->query($sql);
    }

    #数据的操作
    public function  db_delete($sql){
        $this->exec($sql); 
        echo "您的sql语句错误:<br/>";                         #执行exec()
        return $this->mysqli->affected_rows;        #获取受影响的行数
    }

    #数据更新操作
    public  function  db_update($sql){
        $this->exec($sql);                          #执行exec()
        return $this->mysqli->affected_rows;        #获取受影响的行数
    }

    #插入操作
    public function  db_insert($sql){
        $res = $this->exec($sql);                          #执行exec()
        return $this->mysqli->affected_rows;        #获取受影响的行数
    
    }

    #获取单条数据
    public function db_getOne($sql){
        $res = $this->exec($sql);
        return $res = $res->fetch_assoc();
    }

    #获取多条数据
    public function db_getAll($sql){
        $res = $this->exec($sql);
        return $res->fetch_all();
    }

}