PHP封装返回Ajax字符串和JSON数组

<?php
class DBDA
{
    public $host="localhost";
    public $uid = "root";
    public $pwd = "123";
    public $dbname = "mydb";

    //成员方法
    public function Query($sql,$type=1)
    {
        $db = new MySQLi($this->host,$this->uid,$this->pwd,$this->dbname);
        $r = $db->query($sql);

        if($type==1)
        {
            return $r->fetch_all();
        }
        else
        {
            return $r;
        }
    }

    //返回字符串的方法
    public function StrQuery($sql,$type=1)
    {
        $db = new MySQLi($this->host,$this->uid,$this->pwd,$this->dbname);
        $r = $db->query($sql);

        if($type==1)
        {
            $attr = $r->fetch_all();
            $str = "";
            foreach($attr as $v)
            {
                $str .= implode("^",$v)."|";
            }

            return substr($str,0,strlen($str)-1);

        }
        else
        {
            return $r;
        }
    }

    //返回JSON
    function JSONQuery($sql,$type=1)
    {
        $db = new MySQLi($this->host,$this->uid,$this->pwd,$this->dbname);
        $r = $db->query($sql);

        if($type==1)
        {
            return json_encode($r->fetch_all(MYSQLI_ASSOC));
        }
        else
        {
            return $r;
        }
    }
}