Question

愚蠢的问题，我是PHP的新手，参加了一些codeacademy课程，但课程部分对我来说还不是很清楚。我正在尝试解决它，并修改上面的代码。

以下是一个类，它检查用户是否已登录，如果是，则创建用户会话。

class Login
{
    /**
     * @var object The database connection
     */
    private $db_connection = null;
    /**
     * @var array Collection of error messages
     */
    public $errors = array();
    /**
     * @var array Collection of success / neutral messages
     */
    public $messages = array();

    /**
     * the function "__construct()" automatically starts whenever an object of this class is created,
     * you know, when you do "$login = new Login();"
     */
    public function __construct()
    {
        // create/read session, absolutely necessary
        session_start();

        // check the possible login actions:
        // if user tried to log out (happen when user clicks logout button)
        if (isset($_GET["logout"])) {
            $this->doLogout();
        }
        // login via post data (if user just submitted a login form)
        elseif (isset($_POST["login"])) {
            $this->dologinWithPostData();
        }
    }

    /**
     * log in with post data
     */
    private function dologinWithPostData()
    {
        // check login form contents
        if (empty($_POST['user_name'])) {
            $this->errors[] = "Username field was empty.";
        } elseif (empty($_POST['user_password'])) {
            $this->errors[] = "Password field was empty.";
        } elseif (!empty($_POST['user_name']) && !empty($_POST['user_password'])) {

            // create a database connection, using the constants from config/db.php (which we loaded in index.php)
            $this->db_connection = new mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME);

            // change character set to utf8 and check it
            if (!$this->db_connection->set_charset("utf8")) {
                $this->errors[] = $this->db_connection->error;
            }

            // if no connection errors (= working database connection)
            if (!$this->db_connection->connect_errno) {

                // escape the POST stuff
                $user_name = $this->db_connection->real_escape_string($_POST['user_name']);

                // database query, getting all the info of the selected user (allows login via email address in the
                // username field)
                $sql = "SELECT user_name, user_email, user_password_hash
                        FROM sales_users
                        WHERE user_name = '" . $user_name . "' OR user_email = '" . $user_name . "';";
                $result_of_login_check = $this->db_connection->query($sql);

                // if this user exists
                if ($result_of_login_check->num_rows == 1) {

                    // get result row (as an object)
                    $result_row = $result_of_login_check->fetch_object();

                    // using PHP 5.5's password_verify() function to check if the provided password fits
                    // the hash of that user's password
                    if (password_verify($_POST['user_password'], $result_row->user_password_hash)) {

                        // write user data into PHP SESSION (a file on your server)
                        $_SESSION['user_name'] = $result_row->user_name;
                        $_SESSION['user_email'] = $result_row->user_email;
                        $_SESSION['user_login_status'] = 1;

                    } else {
                        $this->errors[] = "Wrong password. Try again.";
                    }
                } else {
                    $this->errors[] = "This user does not exist.";
                }
            } else {
                $this->errors[] = "Database connection problem.";
            }
        }
    }

    /**
     * perform the logout
     */
    public function doLogout()
    {
        // delete the session of the user
        $_SESSION = array();
        session_destroy();
        // return a little feeedback message
        $this->messages[] = "You have been logged out.";

    }

    /**
     * simply return the current state of the user's login
     * @return boolean user's login status
     */
    public function isUserLoggedIn()
    {
        if (isset($_SESSION['user_login_status']) AND $_SESSION['user_login_status'] == 1) {
            return true;
        }
        // default return
        return false;
    }

}

我想要做的是扩展这个类，并使用它从数据库中获取一些其他数据。所以我写道：

class Price extends Login
{
    public function getPrice()
    {

        $sql = "SELECT *
                FROM sales_pricelist";
        $result = $Login->db_connection->query($sql);
        $result = $result->fetch_object();

        echo $result->product_name;

    }

}

我知道这一部分根本不正确。但它说明了我想要实现的目标。所以问题是，正确的版本应该怎么样？我希望在看到确切的例子时我能更好地学习它。

编辑＃1：

此部分$result = $Login->db_connection->query($sql);是否正确？这基本上意味着，我正在从Login类中定位db_connection吗？

编辑＃2：

感谢您的所有评论。

现在，我的Price课程如下：

class Price extends Login
{

    public function __construct() {
            parent::__construct();
    }

    public function getPrice()
    {

        $sql = "SELECT *
                FROM sales_pricelist";
        $result = $this->db_connection->query($sql);
        $result = $result->fetch_object();

        echo $result->product_name;

    }

}

我正试图像这样使用getPrice：

$price = new Price();
$price->getPrice();

但缺少一些东西。这里有什么错误吗？

Answer 1

使用$this引用当前对象。当子类继承parent方法和属性时，您将访问db属性：

$result = $this->db_connection->query($sql);

根据评论进行编辑

如上所述，$db_connection具有私有范围，因此子类无法访问。如果您希望在子类中访问它，您需要将其更改为protected或public，或者在父级中编写具有受保护或公共范围的getter方法：

protected function getDb() { return $this->db_connection; }
重新parent::__construct() 除非您覆盖子类中的方法（通过在其中编写__construct()方法，否则将自动调用父构造函数。如果这样做，您将需要按照所述方式调用父组件;
< / LI>
初始化数据库连接如上所述，db连接在dologinWithPostData()方法中初始化。为了使它对其他方法有用，在父构造函数中初始化它会更有意义。
一般说明这违反了各种良好的OOP原则，例如封装。学习一个体面的现代MVC框架可能会比遵循随机互联网教程更好地奠定基础

Answer 2

乍一看，这对我来说是正确的。你需要的是调用父构造函数。在您的Price类中，以便您可以运行您的登录代码。

function __construct() {
    parent::__construct();
}

PHP - 扩展类（基础知识）

2 个答案: