PHP封装的mysqli数据库操作类示例

<?phpclass db_class{    public $db_url; //连接地址    public $db_username; //连接名    public $db_userpassword; //连接密码    public $db_name; //数据库名    public $db_tablename; //表名    public $db_conn; //数据库连接    public $db_order;    public $db_limit;    public function db_getconn(){ //连接数据库        $this->db_conn= mysqli_connect($this->db_url,$this->db_username,$this->db_userpassword,$this->db_name);        if (!$this->db_conn)        {      echo "连接 MySQL 失败: " . mysqli_connect_error();    }    }    public function __construct($db_url,$db_username,$db_userpassword,$db_name){ //构造方法赋值    $this->db_url=$db_url;        $this->db_username=$db_username;        $this->db_userpassword=$db_userpassword;        $this->db_name=$db_name;        $this->db_order="";        $this->db_limit="";        $this->db_getconn();    mysqli_query($this->db_conn,'set names utf8');    }    public function db_settablename($db_tablename){ //设置表名        $this->db_tablename=$db_tablename;    }    public function db_setorder($str){ //排序操作        $this->db_order="order by $str";    }    public function db_setlimit($start,$end){ //分页操作     $this->db_limit="limit $start,$end";    }    public function db_select($typearr="",$where=""){ //查询操作        if(empty($typearr)){            $typearr="*";        }        else{            $typearr=implode(",",$typearr);        }        if(empty($where)){            $where="";        }else{            $where="where ".$where;        }        $arr=array();        $sql="select $typearr from $this->db_tablename $where $this->db_order $this->db_limit ";        $result = mysqli_query($this->db_conn,$sql);        while($row = $result->fetch_array()) {            $arr[]=$row;        }        return $arr;    }    public function db_update($typearr,$valuearr,$where=""){ //更新操作    $sql="";        if(empty($where)){            $where="";        }else{            $where=" where ".$where;        }        $sql.="update $this->db_tablename set ";         foreach ($typearr as $key=>$value){             if(count($typearr)-1==$key){                 $sql.=$value."='".$valuearr[$key]."'";             }else{                 $sql.=$value."='".$valuearr[$key]."'".",";             }         }        $sql.=$where;    mysqli_query($this->db_conn,$sql);    }    public function db_delete($typestr,$valuestr){ //删除操作    $sql="delete from $this->db_tablename WHERE $typestr=$valuestr";    mysqli_query($this->db_conn,$sql);    }    public function db_insert($typearr,$valuearr){ //插入操作        $sql="insert into $this->db_tablename(".implode(",", $typearr).") values(".implode(",", $valuearr).")";    mysqli_query($this->db_conn,$sql);    }    public function __destruct(){ //析构方法关闭连接        mysqli_close($this->db_conn);    }}