PHP函数中数据库连接对象作用域问题及解决方案

// connection.php 或主脚本文件
$host = 'localhost';
$db   = 'your_database';
$user = 'your_user';
$pass = 'your_password';
$charset = 'utf8mb4';

$dsn = "mysql:host=$host;dbname=$db;charset=$charset";
$options = [
    PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
    PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
    PDO::ATTR_EMULATE_PREPARES   => false,
];
try {
    $conn = new PDO($dsn, $user, $pass, $options);
} catch (\PDOException $e) {
    throw new \PDOException($e->getMessage(), (int)$e->getCode());
}

// 尝试在函数中使用 $conn
function getProductId($product) {
   // 此时 $conn 在此函数作用域内是未定义的
   // $stmt = $conn->prepare(...); // 会导致错误
}

<?php
// ... 数据库连接代码（如上所示），确保 $conn 在全局作用域中已定义 ...

function getProductId($product) {
   global $conn; // 声明 $conn 为全局变量，使其在函数内部可用

   $stmt = $conn->prepare('SELECT idproducts FROM products WHERE title = :product LIMIT 1');
   if ($stmt->execute(array(':product' => $product))) {
      $row = $stmt->fetch(PDO::FETCH_ASSOC);
      return $row['idproducts'];
   }
   return null; // 如果没有找到，返回null或抛出异常
}

// 示例调用
$loadingaid1 = $_REQUEST['loadingaid1'];
$productId = getProductId($loadingaid1);
echo "产品ID: " . $productId;
?>

<?php
// ... 数据库连接代码，确保 $conn 在全局作用域中已定义 ...

function getProductId($product, PDO $conn) { // 声明 $conn 参数，并指定类型为 PDO
   $stmt = $conn->prepare('SELECT idproducts FROM products WHERE title = :product LIMIT 1');
   if ($stmt->execute(array(':product' => $product))) {
      $row = $stmt->fetch(PDO::FETCH_ASSOC);
      return $row['idproducts'];
   }
   return null;
}

// 示例调用
$loadingaid1 = $_REQUEST['loadingaid1'];
$productId = getProductId($loadingaid1, $conn); // 将 $conn 作为参数传入
echo "产品ID: " . $productId;
?>

<?php
class Db {
    private static $instance = null;
    private $conn;

    private function __construct() {
        $host = 'localhost';
        $db   = 'your_database';
        $user = 'your_user';
        $pass = 'your_password';
        $charset = 'utf8mb4';

        $dsn = "mysql:host=$host;dbname=$db;charset=$charset";
        $options = [
            PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
            PDO::ATTR_EMULATE_PREPARES   => false,
        ];
        try {
            $this->conn = new PDO($dsn, $user, $pass, $options);
        } catch (\PDOException $e) {
            throw new \PDOException($e->getMessage(), (int)$e->getCode());
        }
    }

    public static function getInstance() {
        if (self::$instance === null) {
            self::$instance = new Db();
        }
        return self::$instance;
    }

    public function getConnection() {
        return $this->conn;
    }

    // 阻止克隆和反序列化
    private function __clone() {}
    public function __wakeup() {}
}
?>

<?php
// 确保 Db 类已定义并加载
require_once 'Db.php'; // 假设 Db 类在 Db.php 文件中

function getProductId($product) {
   // 通过单例模式获取数据库连接实例
   $conn = Db::getInstance()->getConnection();

   $stmt = $conn->prepare('SELECT idproducts FROM products WHERE title = :product LIMIT 1');
   if ($stmt->execute(array(':product' => $product))) {
      $row = $stmt->fetch(PDO::FETCH_ASSOC);
      return $row['idproducts'];
   }
   return null;
}

// 示例调用
$loadingaid1 = $_REQUEST['loadingaid1'];
$productId = getProductId($loadingaid1);
echo "产品ID: " . $productId;
?>

<?php
// 假设 Db 类有一个直接操作 PDO 对象的方法
class Db {
    // ... (如上所示的单例模式实现) ...

    public function prepare($sql, $options = []) {
        return $this->conn->prepare($sql, $options);
    }
}

function getProductId($product) {
   // 直接通过单例实例调用 prepare 方法
   $stmt = Db::getInstance()->prepare('SELECT idproducts FROM products WHERE title = :product LIMIT 1');
   if ($stmt->execute(array(':product' => $product))) {
      $row = $stmt->fetch(PDO::FETCH_ASSOC);
      return $row['idproducts'];
   }
   return null;
}
// ... 示例调用 ...
?>

<?php
// 假设你有一个DI容器或工厂函数来提供 PDO 实例
// 例如：
// $container = new Container();
// $container->set('db.connection', function() {
//     return new PDO(...);
// });

// 你的服务类，通过构造函数注入依赖
class ProductService {
    private $conn;

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

    public function getProductId($product) {
        $stmt = $this->conn->prepare('SELECT idproducts FROM products WHERE title = :product LIMIT 1');
        if ($stmt->execute([':product' => $product])) {
            $row = $stmt->fetch(PDO::FETCH_ASSOC);
            return $row['idproducts'];
        }
        return null;
    }
}

// 在你的主脚本中
// $conn = $container->get('db.connection'); // 从容器获取连接
// $productService = new ProductService($conn); // 注入连接

// 假设我们直接创建 PDO 实例并注入
$host = 'localhost'; $db = 'your_database'; $user = 'your_user'; $pass = 'your_password'; $charset = 'utf8mb4';
$dsn = "mysql:host=$host;dbname=$db;charset=$charset";
$options = [PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION, PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC, PDO::ATTR_EMULATE_PREPARES => false,];
$conn = new PDO($dsn, $user, $pass, $options);

$productService = new ProductService($conn);
$loadingaid1 = $_REQUEST['loadingaid1'];
$productId = $productService->getProductId($loadingaid1);
echo "产品ID: " . $productId;
?>