AWS Lambda PATCH请求操作DynamoDB报KeyError问题求助

我尝试通过PATCH请求向DynamoDB更新数据，GET和POST请求均可正常工作，但执行PATCH时出现KeyError错误，提示找不到'path'字段。以下是相关信息：

错误信息 #

{
    "errorMessage": "'path'",
    "errorType": "KeyError",
    "requestId": "2d9d09ac-9450-45ab-bbbf-36a92188179c",
    "stackTrace": [
        "  File \"/var/task/lambda_function.py\", line 22, in lambda_handler\n    path = event[\"path\"]\n"
    ]
}

Lambda代码 #

import boto3
import json
from custom_encoder import CustomEncoder

dynamodbProductTable = "prod-status"
dynamodb = boto3.resource("dynamodb")
prodcutTable = dynamodb.Table(dynamodbProductTable)
patchMethod = "PATCH"
productPath = "/product"

def lambda_handler(event, context):
    httpMethod = event["httpMethod"]
    path = event["path"]
    if httpMethod == patchMethod and path == productPath:
        requestBody = json.loads(event["body"])
        response = modifyProduct(requestBody["productId"], requestBody["updateKey"], requestBody["updateValue"])
    else:
        response = buildResponse(404, "Not Found")
    
    return response 

def modifyProduct(productId, updateKey, updateValue):
    try:
        response = prodcutTable.update_item(
            Key={
                "productId": productId
            },

            UpdateExpression="set {0}s = :value".format(updateKey),
            ExpressionAttributeValues={
                ":value": updateValue
            },
            ReturnValues="UPDATED_NEW"
        )
        body = {
            "Operation": "UPDATE",
            "Message": "SUCCESS",
            "UpdatedAttributes": response
        }
        return buildResponse(200, body)
    except:
        logger.exception("error in modifyProduct")

def buildResponse(statusCode, body=None):
    response = {
        "statusCode": statusCode,
        "headers": {
            "Content-Type": "application/json",
            "Access-Control-Allow-Origin": "*"
        }
    }

    if body is not None:
        response["body"] = json.dumps(body, cls=CustomEncoder)
    return response

自定义编码器代码 #

import json
from decimal import Decimal 

class CustomEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, Decimal):
            return float(obj)
        
        return json.JSONEncoder.default(self, obj)

1. 安全获取event字段，避免KeyError #

直接通过event["path"]访问字段会在字段缺失时抛出异常，改用event.get()方法安全获取，并添加缺失字段的处理逻辑：
修改lambda_handler函数开头代码：

def lambda_handler(event, context):
    httpMethod = event.get("httpMethod", "")
    path = event.get("path", "")
    
    # 校验必填字段是否存在
    if not httpMethod or not path:
        return buildResponse(400, "请求参数缺失：httpMethod或path字段不存在")
    
    if httpMethod == patchMethod and path == productPath:
        # 安全解析请求体，避免body为空的情况
        requestBody = json.loads(event.get("body", "{}"))
        # 校验请求体必填字段
        required_fields = ["productId", "updateKey", "updateValue"]
        if not all(key in requestBody for key in required_fields):
            return buildResponse(400, f"请求体缺失必填字段：{', '.join(required_fields)}")
        
        response = modifyProduct(requestBody["productId"], requestBody["updateKey"], requestBody["updateValue"])
    else:
        response = buildResponse(404, "Not Found")
    
    return response 

2. 检查API Gateway集成配置 #

如果Lambda通过API Gateway触发，确保PATCH请求的集成规则和GET/POST一致：

• 确认使用Lambda代理集成：该模式下API Gateway会自动将httpMethod、path、body等请求信息封装到event中传递给Lambda，无需手动配置映射。
• 若使用自定义集成，需在PATCH请求的集成模板中添加"path": "$context.path"配置，确保path字段被正确传入event。

3. 修复UpdateExpression的字段名错误 #

原代码中UpdateExpression多了一个多余的s，会导致更新的字段名错误（例如updateKey为status时，会变成statuss），修改为：

UpdateExpression="set {0} = :value".format(updateKey),

4. 修复日志模块未定义问题 #

modifyProduct函数中使用了logger.exception但未初始化日志模块，需在Lambda代码开头添加日志配置：

import logging
logger = logging.getLogger()
logger.setLevel(logging.INFO)

内容的提问来源于stack exchange，提问作者Vardhan