AWS AppSync VTL模板foreach内嵌if语句报错问题咨询

问题描述 #

我有一个AWS AppSync VTL模板，在#foreach块内部使用#if语句时出现报错，想咨询两个问题：

1. 当前使用的语法是否正确？
2. 若语法不正确，该如何编写此代码？

我曾尝试使用#if($method.type == "us_bank_account")的写法，但同样无法正常运行。

当前VTL代码 #

#foreach($method in $body.paymentMethods)
    #set($transformedMethod = {
        "Id": $method.id,
        "Object": $method.object,
        "BillingDetails": {
            "Email": $method.billing_details.email,
            "Name": $method.billing_details.name,
            "Phone": $method.billing_details.phone
        },
        "Created": $method.created,
        "Customer": $method.customer,
        "Livemode": $method.livemode,
        "Metadata": $utils.toJson($method.metadata),
        "Type": $method.type,
        #if($method.type.equals("us_bank_account"))
        "USBankAccount": {
            "AccountHolderType": $method.us_bank_account.account_holder_type,
            "AccountType": $method.us_bank_account.account_type,
            "BankName": $method.us_bank_account.bank_name,
            "FinancialConnectionsAccount": $method.us_bank_account.financial_connections_account,
            "Fingerprint": $method.us_bank_account.fingerprint,
            "Last4": $method.us_bank_account.last4,
            "Networks": {
                "Preferred": $method.us_bank_account.networks.preferred,
                "Supported": $utils.toJson($method.us_bank_account.networks.supported)
            },
            "RoutingNumber": $method.us_bank_account.routing_number,
            "StatusDetails": $method.us_bank_account.status_details
        }
        #end
    })
    $util.qr($paymentMethods.add($transformedMethod))
#end

源JSON数据 #

{
    "isSuccess": true,
    "paymentMethods": [
        {
            "billing_details": {
                "address": {
                    "city": null,
                    "country": null,
                    "line1": null,
                    "line2": null,
                    "postal_code": null,
                    "state": null
                },
                "email": null,
                "name": "Test Account Holder",
                "phone": null
            },
            "created": 1701975288,
            "customer": "cus_P60pU8eyi7OM1T",
            "id": "pm_1OKmiiApDBfa1h4dHUrVeVhm",
            "livemode": false,
            "metadata": {},
            "object": "payment_method",
            "type": "us_bank_account",
            "us_bank_account": {
                "account_holder_type": "individual",
                "account_type": "checking",
                "bank_name": "STRIPE TEST BANK",
                "financial_connections_account": null,
                "fingerprint": "vFaCL0w3N7j2qWhO",
                "last4": "6789",
                "networks": {
                    "preferred": "ach",
                    "supported": [
                        "ach"
                    ]
                },
                "routing_number": "110000000",
                "status_details": {}
            }
        },
        {
            "billing_details": {
                "address": {
                    "city": "Libertyville",
                    "country": "US",
                    "line1": "1401 Franklin Blvd.",
                    "line2": null,
                    "postal_code": "60048",
                    "state": "IL"
                },
                "email": null,
                "name": "Test",
                "phone": null
            },
            "card": {
                "brand": "visa",
                "checks": {
                    "address_line1_check": "pass",
                    "address_postal_code_check": "pass",
                    "cvc_check": null
                },
                "country": "US",
                "exp_month": 12,
                "exp_year": 2027,
                "fingerprint": "cNo8pU2BD7OMVNAa",
                "funding": "credit",
                "generated_from": null,
                "last4": "4242",
                "networks": {
                    "available": [
                        "visa"
                    ],
                    "preferred": null
                },
                "three_d_secure_usage": {
                    "supported": true
                },
                "wallet": null
            },
            "created": 1701974966,
            "customer": "cus_P60pU8eyi7OM1T",
            "id": "card_1OKmdWApDBfa1h4d0WRWWO7W",
            "livemode": false,
            "metadata": {},
            "object": "payment_method",
            "type": "card"
        }
    ]
}

问题解答 #

1. 当前语法是否正确？ #

当前语法存在两个核心问题：

• JSON结构语法错误：#if块前后的键值对会引发逗号问题——条件不满足时，"Type": $method.type,末尾的逗号会导致JSON格式无效；条件满足时，USBankAccount块末尾无后续键值对也会触发语法错误。
• 空值处理缺失：若$method.type为null，调用.equals()方法会直接抛出空指针异常；使用==比较字符串虽可行，但同样未处理空值场景。

2. 修正后的代码写法 #

通过拆分对象构建逻辑、增加空值判断来解决问题：

#foreach($method in $body.paymentMethods)
    #set($transformedMethod = {
        "Id": $method.id,
        "Object": $method.object,
        "BillingDetails": {
            "Email": $method.billing_details.email,
            "Name": $method.billing_details.name,
            "Phone": $method.billing_details.phone
        },
        "Created": $method.created,
        "Customer": $method.customer,
        "Livemode": $method.livemode,
        "Metadata": $utils.toJson($method.metadata),
        "Type": $method.type
    })
    #if($method.type && $method.type == "us_bank_account")
        #set($void = $transformedMethod.put("USBankAccount", {
            "AccountHolderType": $method.us_bank_account.account_holder_type,
            "AccountType": $method.us_bank_account.account_type,
            "BankName": $method.us_bank_account.bank_name,
            "FinancialConnectionsAccount": $method.us_bank_account.financial_connections_account,
            "Fingerprint": $method.us_bank_account.fingerprint,
            "Last4": $method.us_bank_account.last4,
            "Networks": {
                "Preferred": $method.us_bank_account.networks.preferred,
                "Supported": $utils.toJson($method.us_bank_account.networks.supported)
            },
            "RoutingNumber": $method.us_bank_account.routing_number,
            "StatusDetails": $method.us_bank_account.status_details
        }))
    #end
    $util.qr($paymentMethods.add($transformedMethod))
#end

关键修正点说明 #

• 拆分对象构建：先创建无条件属性的基础对象，再通过$transformedMethod.put()动态添加USBankAccount属性，彻底规避JSON逗号语法错误。
• 空值安全判断：#if($method.type && $method.type == "us_bank_account")先检查$method.type是否存在，再做字符串比较，防止空指针异常。
• 屏蔽返回值：$transformedMethod.put()会返回旧值，用#set($void = ...)避免输出不必要的内容。

内容的提问来源于stack exchange，提问作者Denil Parmar