PHP表单提交消息延迟显示：Post-Redirect-Get模式深度解析与实践

if ($res_bookings){
    $_SESSION['done'] = "<h2 class='success'>BOOKED SUCCESSFULLY</h2>";
} else {
    $_SESSION['done'] = "<h2 class='failed'>BOOKING FAILED</h2>";
}

// 假设 $res_bookings 是数据库操作的结果
if ($res_bookings){
    echo "<h2 class='success'>BOOKED SUCCESSFULLY</h2>";
} else {
    echo "<h2 class='failed'>BOOKING FAILED</h2>";
}
// 在验证失败时也直接输出并终止
if($customer_name == ""){
    echo "<p class='failed'>PLEASE FILL NAME</p>";
    die(); // 或者 exit();
}

<?php
session_start();
// ... 页面其余代码
?>

<?php
session_start(); // 确保在任何输出之前启动session

// 假设 $conn 已经连接到数据库
// 示例：$conn = new mysqli("localhost", "user", "password", "database");

// --- 消息显示逻辑 ---
// 在页面顶部显示任何待处理的消息，并清除session变量
function displayAndClearSessionMessage($sessionKey) {
    if (isset($_SESSION[$sessionKey])) {
        echo $_SESSION[$sessionKey];
        unset($_SESSION[$sessionKey]); // 消息显示后立即清除
    }
}

// 显示所有可能的反馈消息
displayAndClearSessionMessage('done');
displayAndClearSessionMessage('name_error'); // 对应 'name' 验证
displayAndClearSessionMessage('contacts_error'); // 对应 'contacts' 验证
displayAndClearSessionMessage('menu_error'); // 对应 'menu' 验证
// --- 消息显示逻辑结束 ---

// --- 表单提交处理逻辑 ---
if(isset($_POST['submit'])){
    // 1. 获取并清理表单数据
    $customer_name = mysqli_real_escape_string($conn, $_POST['customer_name']);
    $customer_number = mysqli_real_escape_string($conn ,$_POST['customer_number']);
    $customer_email = mysqli_real_escape_string($conn, $_POST['customer_email']);
    $event_type = mysqli_real_escape_string($conn, $_POST['event']);
    $start = mysqli_real_escape_string($conn, $_POST['event_start']);
    $end = mysqli_real_escape_string($conn, $_POST['event_end']);
    $address = mysqli_real_escape_string($conn, $_POST['event_address']);
    $menus = $_POST['menu'] ?? []; // 使用 ?? 避免未设置时的警告
    $extras = $_POST['extra'] ?? []; // 使用 ?? 避免未设置时的警告

    // 2. 数据验证
    if($customer_name == ""){
        $_SESSION['name_error'] = "<p class='failed'>PLEASE FILL NAME</p>";
        header('Location: ' . $_SERVER['PHP_SELF']); // 重定向回当前页面
        exit();
    }

    if($customer_number == "" && $customer_email == ""){
        $_SESSION['contacts_error'] = "<p class='failed'>PLEASE FILL CONTACTS</p>";
        header('Location: ' . $_SERVER['PHP_SELF']);
        exit();
    }

    if(empty($menus) || empty($extras)){
        $_SESSION['menu_error'] = "<p class='failed'>PLEASE PICK YOUR MENU OR EXTRAS</p>";
        header('Location: ' . $_SERVER['PHP_SELF']);
        exit();
    }

    // 生成随机ID (在实际生产中，更推荐使用UUID或数据库自增ID)
    $booking_id = rand(1000, 9999); // 确保ID有足够的位数，避免000-999的重复率
    $event_id = rand(1000, 9999);
    $payment_id = rand(1000, 9999);

    // 3. 数据库操作 (简化错误处理，实际应用中需更严谨)
    $all_operations_successful = true; // 标记所有数据库操作是否成功

    // 开启事务 (重要：确保多表操作的原子性)
    $conn->begin_transaction();
    try {
        // --- 插入 event_details ---
        $query = "INSERT INTO event_details SET id = ?, startTime = ?, endTime = ?, eventAddress = ?, event_type = (SELECT id FROM events WHERE id = ?)";
        $stmt = $conn->prepare($query);
        $stmt->bind_param("isssi", $event_id, $start, $end, $address, $event_type);
        if (!$stmt->execute()) {
            throw new Exception($conn->error);
        }

        // --- 创建 booking record ---
        $query_2 = "INSERT INTO bookings SET id = ?, customer_name = ?, customer_contact_no = ?, customer_email = ?, eventID = (SELECT id FROM event_details WHERE id = ?)";
        $stmt_2 = $conn->prepare($query_2);
        $stmt_2->bind_param("isssi", $booking_id, $customer_name, $customer_number, $customer_email, $event_id);
        if (!$stmt_2->execute()) {
            throw new Exception($conn->error);
        }

        // --- 创建 menu record ---
        $menu_query = "INSERT INTO menus_bookings SET bookingID = (SELECT id FROM bookings WHERE id = ?), type = (SELECT id FROM menus_types WHERE id = ?)";
        $menu_stmt = $conn->prepare($menu_query);
        $menu_stmt->bind_param("ii", $booking_id, $menu_item_id); // 变量名需与foreach中的匹配
        foreach ($menus as $menu_item_id){ // 循环变量名修改
           if (!$menu_stmt->execute()) {
               throw new Exception($conn->error);
           }
        }

        // --- 创建 extras record ---
        $extras_query = "INSERT INTO extras_bookings SET bookingID = (SELECT id FROM bookings WHERE id = ?), type = (SELECT id FROM extras_types WHERE id = ?)";
        $extras_stmt = $conn->prepare($extras_query);
        $extras_stmt->bind_param("ii", $booking_id, $extra_item_id); // 变量名需与foreach中的匹配
        foreach ($extras as $extra_item_id){ // 循环变量名修改
            if (!$extras_stmt->execute()) {
                throw new Exception($conn->error);
            }
        }

        // --- 计算费用 ---
        $menu_total = 0;
        if (!empty($menus)) {
            $menu_sql = "SELECT SUM(mt.price) as 'menu total' FROM menus_types mt JOIN menus_bookings mb ON mt.id = mb.type WHERE mb.bookingID = ?";
            $stmt_menu = $conn->prepare($menu_sql);
            $stmt_menu->bind_param("i", $booking_id);
            $stmt_menu->execute();
            $result_menu = $stmt_menu->get_result();