如何運行mysqli查詢？

Question

       <?php

// Forum Configuration
define('DB_HOST','localhost'); // Database Hostname
define('DB_USER','root'); // Database Username
define('DB_PASSWORD',''); // Database Password
define('DB_NAME','ultraforum'); // Database Name
define('WEB_NAME','Website Name'); // Website Name
define('WEB_TITLE','Website Title'); // Website Title

// Do not modify anything under this line :)

    class db {

    var $dbhost;
    var $dbuser;
    var $dbpassword;
    var $dbname;
    var $query;

        function connect() {

            $this->db = 
                new mysqli($this->dbhost, $this->dbuser, $this->dbpassword, $this->dbname);

        }

        function __construct() {
            $this->dbhost = DB_HOST;
            $this->dbuser = DB_USER;
            $this->dbpassword = DB_PASSWORD;
            $this->dbname = DB_NAME;
        }

    }

    $con = new db;
    $con->connect();
    $con->query("SELECT * FROM topics");

仍然無法正常工作，並給我一個錯誤致命錯誤：在第39行的C：\\ wamp \\ www \\ CodeCanyon \\ Ultra Forum \\ core \\ Config.php中調用未定義的方法db :: query（）

我只是從php面向對象編程開始，我做了連接類（使用mySQLi ），但是我仍然不明白如何運行查詢？

Answer 1

$con = new db;
$con->connect();
$con->db->query("SELECT * FROM topics");

但是這堂課似乎還沒用。

Answer 2

嘗試這個

   $con->db->query("SELECT * FROM topics");