php - OOP PHP undefined variable 和空查询

Question

我正在尝试通过查询测试数据库来学习 OOP PHP。我尝试用谷歌搜索答案，但没有成功。这是我的代码:

<?php

class DB {

        protected $db;
        protected $query;

        public function __construct() {
            $this->db = new mysqli("localhost","root","","test2");
            $this->query = "SELECT * FROM test";
        }


        public function querydb() {
            $this->db->query($db,$query);
        }

    }

    $database = new DB();
    $database->querydb();


?>

它表示构造函数中定义的两个变量未定义，并且查询为空。有什么建议吗？

Answer 1

更改:

$this->db->query($db,$query);

致:

$this->db->query($this->query);

试试这个:

<?php

class DB {

        protected $db;
        protected $query;

        public function __construct() {
            $this->db = new mysqli("localhost","root","","test2");
            $this->query = "SELECT * FROM test";
        }


        public function querydb() {
            $this->db->query($this->query);
        }

    }

    $database = new DB();
    $database->querydb();


?>