PHP递增操作符与HTML表单的自动填充_PHP表单递增字段处理

<form method="post" action="add_product.php">
  <label>产品编号：</label>
  <input type="text" name="product_id" value="<?php echo htmlspecialchars($nextId); ?>" readonly>

  <label>产品名称：</label>
  <input type="text" name="product_name">

  <button type="submit">添加产品</button>
</form>

// 假设从数据库获取当前最大ID
$currentId = (int)$row['max_id']; // 如：100
$nextId = ++$currentId; // 结果为101

if ($_POST) {
    $productId = (int)$_POST['product_id'];
    $productName = trim($_POST['product_name']);

    // 验证数据
    if (!empty($productName)) {
        // 插入数据库
        $stmt = $pdo->prepare("INSERT INTO products (id, name) VALUES (?, ?)");
        $stmt->execute([$productId, $productName]);

        // 成功后准备下一个ID
        $nextId = $productId + 1;
    }
}

session_start();
if (!isset($_SESSION['next_id'])) {
    // 首次加载，从数据库取最大ID
    $stmt = $pdo->query("SELECT MAX(id) AS max_id FROM products");
    $row = $stmt->fetch();
    $_SESSION['next_id'] = (int)$row['max_id'] + 1;
}

$nextId = $_SESSION['next_id'];

// 提交成功后更新
if ($_POST && $success) {
    $_SESSION['next_id']++;
}