PHP封装返回Ajax字符串和JSON数组的方法

<?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;
    }
  }
}