php定义类查询mysql

<?php
class Database {
    private $host = 'localhost';
    private $db_name = 'test_db';
    private $username = 'root';
    private $password = '';
    public $conn;

    public function getConnection() {
        $this->conn = null;
        try {
            $this->conn = new PDO("mysql:host=" . $this->host . ";dbname=" . $this->db_name, $this->username, $this->password);
            $this->conn->exec("set names utf8");
        } catch(PDOException $exception) {
            echo "Connection error: " . $exception->getMessage();
        }
        return $this->conn;
    }
}

class User {
    private $conn;
    private $table_name = "users";

    public $id;
    public $username;
    public $email;

    public function __construct($db) {
        $this->conn = $db;
    }

    public function read() {
        $query = "SELECT * FROM " . $this->table_name . " WHERE id = ?";
        $stmt = $this->conn->prepare($query);
        $stmt->bindParam(1, $this->id);
        $stmt->execute();
        $row = $stmt->fetch(PDO::FETCH_ASSOC);
        $this->username = $row['username'];
        $this->email = $row['email'];
    }
}

// 使用示例
$database = new Database();
$db = $database->getConnection();
$user = new User($db);
$user->id = 1;
$user->read();
echo "Username: " . $user->username . "<br>";
echo "Email: " . $user->email;
?>