PHP array_filter使用问题：无法提取Namecheap数据中的注册价格

问题背景 #

我是PHP新手，需要从Namecheap沙箱返回的大型数组中，提取指定域名后缀（TLD）对应「register」产品分类下的1年注册价格。我写了对应的代码，但运行时持续报错，不过通过硬编码数组路径可以成功获取目标价格。

我的代码 #

class registerPrice {
    function getRegisterPrice($domainTLD, $newArr) {
        // Extract the "Register" product category for the target TLD
        $registerCategory = array_filter($newArr['CommandResponse']['UserGetPricingResult']['ProductType'], function ($category) use ($domainTLD) {
            return $category['@attributes']['Name'] === 'register' && $category['Product']['@attributes']['Name'] === $domainTLD;
        });

        // Extract the prices for the 1-year duration from the "register" category for the target TLD
        $registerPrices = array_column($registerCategory, 'Product');
        $registerPriceForOneYear = null;
        foreach ($registerPrices as $product) {
            foreach ($product as $price) {
                if ($price['@attributes']['Duration'] == 1 && $price['@attributes']['DurationType'] == 'YEAR') {
                    $registerPriceForOneYear = $price['Price']['@attributes']['Price'];
                    break 2; // Exit both loops once the price for 1 year is found
                }
            }
        }
        return $registerPriceForOneYear;
    }   
}

数组结构片段 #

Array
(
    [@attributes] => Array
        (
            [Status] => OK
        )

    [Errors] => Array
        (
        )

    [Warnings] => Array
        (
        )

    [RequestedCommand] => namecheap.users.getpricing
    [CommandResponse] => Array
        (
            [@attributes] => Array
                (
                    [Type] => namecheap.users.getPricing
                )

            [UserGetPricingResult] => Array
                (
                    [ProductType] => Array
                        (
                            [@attributes] => Array
                                (
                                    [Name] => domains
                                )

                            [ProductCategory] => Array
                                (
                                    [0] => Array
                                        (
                                            [@attributes] => Array
                                                (
                                                    [Name] => reactivate
                                                )

                                            [Product] => Array
                                                (
                                                    [@attributes] => Array
                                                        (
                                                            [Name] => com
                                                        )

                                                    [Price] => Array
                                                        (
                                                            [@attributes] => Array
                                                                (
                                                                    [Duration] => 1
                                                                    [DurationType] => YEAR
                                                                    [Price] => 13.48
                                                                    [Currency] => USD
                                                                )

                                                        )

                                                )

                                        )

                                    [1] => Array
                                        (
                                            [@attributes] => Array
                                                (
                                                    [Name] => register
                                                )

                                            [Product] => Array
                                                (
                                                    [@attributes] => Array
                                                        (
                                                            [Name] => com
                                                        )

                                                    [Price] => Array
                                                        (
                                                            [0] => Array
                                                                (
                                                                    [@attributes] => Array
                                                                        (
                                                                            [Duration] => 1
                                                                            [DurationType] => YEAR
                                                                            [Price] => 10.28
                                                                            [Currency] => USD
                                                                        )

                                                                )

                                                        )

                                                )

                                        )

                                )

                        )

                )

        )

)

错误信息 #

PHP Warning:  Undefined array key "@attributes" in D:\xampp\htdocs\sm\registrationPrice.php on line 6

Warning: Undefined array key "@attributes" in D:\xampp\htdocs\sm\registrationPrice.php on line 6

Warning: Trying to access array offset on value of type null in D:\xampp\htdocs\sm\registrationPrice.php on line 6

Warning: Undefined array key "@attributes" in D:\xampp\htdocs\sm\registrationPrice.php on line 6

Warning: Trying to access array offset on value of type null in D:\xampp\htdocs\sm\registrationPrice.php on line 6

第6行代码：return $category['@attributes']['Name'] === 'register' && $category['Product']['@attributes']['Name'] === $domainTLD;

原因分析 #

1. 遍历层级错误：当前用array_filter遍历的是ProductType数组，而该数组包含两个元素：@attributes（产品类型标识，值为domains）和ProductCategory（所有产品分类的数组）。当遍历到@attributes元素时，它本身没有@attributes子键，也没有Product键，直接访问就会触发未定义键警告。
2. 缺少存在性检查：即使遍历正确的数组，也可能存在部分分类结构不完整的情况，直接访问深层数组键会导致警告。

解决方法 #

1. 修正遍历目标：将array_filter的目标改为ProductType下的ProductCategory数组，这才是包含各个分类（如register、reactivate）的数组。
2. 添加数组键存在性检查：在访问数组键之前，用isset()确认键存在，避免警告。

修正后的代码 #

class registerPrice {
    function getRegisterPrice($domainTLD, $newArr) {
        // 确认基础数组路径存在，避免后续报错
        if (!isset($newArr['CommandResponse']['UserGetPricingResult']['ProductType']['ProductCategory'])) {
            return null;
        }

        // 遍历正确的ProductCategory数组，筛选register分类和指定TLD
        $registerCategory = array_filter($newArr['CommandResponse']['UserGetPricingResult']['ProductType']['ProductCategory'], function ($category) use ($domainTLD) {
            // 先检查必要键是否存在
            if (!isset($category['@attributes']['Name'], $category['Product']['@attributes']['Name'])) {
                return false;
            }
            return $category['@attributes']['Name'] === 'register' && $category['Product']['@attributes']['Name'] === $domainTLD;
        });

        $registerPriceForOneYear = null;
        foreach ($registerCategory as $category) {
            // 处理Price数组的两种情况：单个价格或多个价格数组
            $prices = is_array($category['Product']['Price']) ? $category['Product']['Price'] : [$category['Product']['Price']];
            foreach ($prices as $price) {
                if (isset($price['@attributes']['Duration'], $price['@attributes']['DurationType']) 
                    && $price['@attributes']['Duration'] == 1 
                    && $price['@attributes']['DurationType'] == 'YEAR'
                    && isset($price['@attributes']['Price'])) {
                    $registerPriceForOneYear = $price['@attributes']['Price'];
                    break 2;
                }
            }
        }
        return $registerPriceForOneYear;
    }   
}

内容的提问来源于stack exchange，提问作者Bryan Corringham