Bug: with a DynamoDB composite key, DataRecord.idempotency_key is the static partition key value #8724

Expected Behaviour

With a composite key (sort_key_attr set), DataRecord.idempotency_key is the record's own key, the value stored in the sort key, so the local cache, the response_hook and the IdempotencyAlreadyInProgressError message refer to the actual record.

Current Behaviour

DynamoDBPersistenceLayer._item_to_data_record sets idempotency_key=data[self.key_attr], which with a composite key is the static partition key value (static_pk_value, idempotency#<function> by default) for every record. So use_local_cache stores every record under one key and never hits for records written elsewhere, the response_hook receives idempotency_key='idempotency#myfn' (the docs example reads that field), and the in-progress error message shows the static value.

Code snippet

from aws_lambda_powertools.utilities.idempotency import DynamoDBPersistenceLayer

layer = DynamoDBPersistenceLayer(table_name="t", sort_key_attr="sk", static_pk_value="idempotency#fn")
record = layer._item_to_data_record(
    {"id": {"S": "idempotency#fn"}, "sk": {"S": "fn#abc"}, "status": {"S": "COMPLETED"}, "expiration": {"N": "9999999999"}, "data": {"S": "{}"}},
)
record.idempotency_key  # 'idempotency#fn', expected 'fn#abc'

For the public-API test, use botocore.stub.Stubber on the layer's client like the existing composite-key tests do, and assert on what the response_hook receives.

Possible Solution

In aws_lambda_powertools/utilities/idempotency/persistence/dynamodb.py, _item_to_data_record: idempotency_key=data[self.sort_key_attr] if self.sort_key_attr else data[self.key_attr]. Add a test with sort_key_attr and a response_hook asserting the key, and one for the local cache hit.

Item 7 of the Idempotency audit in #8603. No AWS resources needed, the existing tests stub DynamoDB.

Powertools for AWS Lambda (Python) version

latest

AWS Lambda function runtime

3.13

Packaging format used

PyPi

Debugging logs

No response