PHP特性如何满足多用户商城系统的开发需求？

class User {
    private $username;
    private $password;
    private $email;
    
    // 构造函数
    public function __construct($username, $password, $email) {
        $this->username = $username;
        $this->password = $password;
        $this->email = $email;
    }
    
    // 设置用户名
    public function setUsername($username) {
        $this->username = $username;
    }
    
    // 获取用户名
    public function getUsername() {
        return $this->username;
    }
    
    // 其他方法...
}

// 连接MySQL数据库
$mysqli = new mysqli("localhost", "username", "password", "database");

// 查询用户信息
$query = "SELECT * FROM users WHERE id = 1";
$result = $mysqli->query($query);
$row = $result->fetch_assoc();

// 插入新用户
$query = "INSERT INTO users (username, password, email) VALUES ('John', '123456', 'john@example.com')";
$mysqli->query($query);

// 启动会话
session_start();

// 设置用户ID
$_SESSION['user_id'] = 1;

// 获取用户ID
$user_id = $_SESSION['user_id'];

// 销毁会话
session_destroy();

// 使用预处理语句查询用户信息
$query = "SELECT * FROM users WHERE username = ?";
$stmt = $mysqli->prepare($query);
$stmt->bind_param("s", $username);
$stmt->execute();
$result = $stmt->get_result();

// 插入新用户（使用预处理语句）
$query = "INSERT INTO users (username, password, email) VALUES (?, ?, ?)";
$stmt = $mysqli->prepare($query);
$stmt->bind_param("sss", $username, $password, $email);
$stmt->execute();