(step-functions): (add keyPath in item reader)

[Nicolas-SB]

Describe the feature

Analogous to the new bucketNamePath parameter introduced in #31619 I expected to find a keyPath parameter when creating a item reader.

If the already existing "key" parameter is supposed to implicitly support JsonPath, then the naming and docstring of the parameter does not clearly express that.

Use Case

I get an input event containing the dynamically generated key of the manifest file and want to reference it. The constructor of the class, in my case S3JsonItemReader, is vague about how to achieve this. In the AWS console for step functions I can just give it a JsonPath, the CDK constructor tells me to give it a concrete key.

Proposed Solution

Either add a new parameter key_path analogous to bucket_name_path or update the docstring of parameter key to point out clearly that JsonPath is supported.

Other Information

On a side-note, the docstring of bucket and bucket_name_path tells me the default is "S3 bucket will be determined from" - I do not quite understand what this is supposed to tell me

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

CDK version used

2.173.2

Environment details (OS name and version, etc.)

macOS Sequoia 15.2

[khushail]

Hi @Nicolas-SB , thanks for reaching out. I see that in the AWS Stepfunction README file, it looks like the JSON Path is supported for the parameterkey -

https://github.com/aws/aws-cdk/blob/v2.173.2/packages/aws-cdk-lib/aws-stepfunctions/README.md

Hope this is what you are looking for. Let me know if your ask is different.

[Nicolas-SB]

Thanks for the quick answer! I am working with python CDK and the S3JsonItemReader class looks the following:

According to the description it seems like key would not support JsonPath. For the bucket there seems to be one parameter specifically for a predefined bucket and one specifically for a JsonPath. Therefore I assumed that the key parameter only supports a predefined key and the class is missing a parameter for a JsonPath.

I guess this misunderstanding could be resolved by adjusting the description to mention that JsonPath is supported.

[Nicolas-SB]

Edit:

I got it working using the code:

sfn.S3JsonItemReader(
    bucket_name_path=sfn.JsonPath.string_at("$.manifest_bucket"),
    key=sfn.JsonPath.string_at("$.data_manifest_key"),
)

So it is supported, but I stand by my point that the explanation contained in the docstring (see comment above) is rather misleading and does a poor job of explaining how to use the class.

---

Something does not seem to be quite right. I have the following python cdk code:

sfn.DistributedMap(
  scope=scope,
  id="my_id",
  item_reader=sfn.S3JsonItemReader(bucket_name_path="$.manifest_bucket", key="$.data_manifest_key")
)

Which produces a DistributedMap with the following setting:

In the console it works once I select this setting:

It seems like this setting is currently not supported by Python CDK?

[khushail]

@Nicolas-SB , I see that you got it working in Typescript so it should work in python as well. I will try to repro this in python and share the code.

However I agree that there should have been clear explanation reg. Key JSONPATH. So marking it as P3 which means community contributions are welcome in this regard.