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Bug: multiValueQueryStringParameters interferes with queryStringParameters #7993
Description
Expected Behaviour
When using both queryStringParameters and multiValueQueryStringParameters I expect all annotated query parameters to be set in my router handler.
Current Behaviour
If multiValueQueryStringParameters is used for one parameter and queryStringParameters for another, the latter will not be set in the router handler.
Code snippet
from typing import Annotated, Optional
from aws_lambda_powertools.event_handler.openapi.params import Query
@router.get("/foobar")
def foobar(
ids: Annotated[Optional[list[str]], Query()] = None,
status: Annotated[Optional[str], Query()] = None,
):
assert ids # This passes
assert status is not None # This fails
def test_issue():
event = {
"multiValueQueryStringParameters": {"ids": ["1", "2", "3"]},
"queryStringParameters": {"status": "fizzbuzz"},
}
# Actually uses rest resolver
response = handler(event, lambda_context)Possible Solution
No response
Steps to Reproduce
Run test provided in code snippet.
Powertools for AWS Lambda (Python) version
3.21.0
AWS Lambda function runtime
3.13
Packaging format used
PyPi
Activity
aalvrz commentedon Feb 11, 2026
I don't understand if only one should be used and if so, which one?
leandrodamascena commentedon Apr 6, 2026
Hey @aalvrz, first of all - I'm really sorry for the delay on this one.
I've investigated the root cause and here's what's happening is because in
APIGatewayProxyEvent.resolved_query_string_parameters, we have:When
multiValueQueryStringParametersis present and non-empty (truthy), we return only that dict and completely ignorequeryStringParameters. In your case,idslives inmultiValueQueryStringParametersandstatuslives inqueryStringParameters- sostatusgets dropped.The same pattern exists in
ALBEvent.Instead of an
orthat picks one or the other, we'll merge both: usemultiValueQueryStringParametersas the base and fill in any missing keys fromqueryStringParameters. This way no parameter gets lost regardless of which field it appears in.I'll include this fix in the next release. Thanks for the detailed reproduction - it made this straightforward to track down.
aalvrz commentedon Apr 6, 2026
Thanks @leandrodamascena !
powertools-for-aws-oss-automation commentedon Apr 14, 2026
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github-actions commentedon Apr 14, 2026
This is now released under 3.28.0 version!