Serverless alb event does not have query params as a list with multiValueQueryStringParameters: true

Question

So i have a serverless app where i am sending the request to an alb which gets redirected to a lambda function. My request is /?filePath=a&filePath=b&filePath=c&filePath=d&pageSize=2 but in the event being passed to the lambda its shown as below:-

  {
  "requestContext": {
      "elb": {
          "targetGroupArn": "xyz"
       }
   },
   "httpMethod": "GET",
   "path": "/xyz",
   "queryStringParameters": {
      "filePath": "d",
      "page": "1",
   },

So, essentially instead of taking all the input files as a list in event.mutliValueStringQueryParameters: ['a', 'b', 'c', 'd'], its taking only the last element as the queryParam. My serverless alb event for this API is this:-

- alb:
  listenerArn: XXX
  priority: 2
  multiValueQueryStringParameters: true
  conditions:
    path: XXX
  method: GET
- http:
  path: XXX
  method: GET

Any help is appreciated.

Answer 1

I haven't tried this myself but I think you need to use a proxy integration to get the multiValueQueryStringParameters field.

https://aws.amazon.com/blogs/compute/support-for-multi-value-parameters-in-amazon-api-gateway/

https://docs.aws.amazon.com/apigateway/latest/developerguide/set-up-lambda-proxy-integrations.html

Note, when selecting an integration you can choose the payload version. If you select 2 there are no such proxy restrictions but instead of getting multiValueQueryStringParameters your values are concatenated together in a comma-delimited list.

"filePath" : "a,b,c,d"