Read value from json in workflow template without loop

[bmacera]

Hi,

I'm trying to read parameters from json in a workflow template. What I mean :

• I have a short template which just produces a json with year and year-1 as shown above

- name: t-get-prev-year
    inputs:
      parameters:
      - name: year
    script:
      image: my-python-docker
      command: [python]
      source: |
        import json
        import sys
        json.dump([{"year": {{inputs.parameters.year}}, "prev-year": ({{inputs.parameters.year}}-1)}], open("/outputdir/years.json", "w"))

    outputs:
      parameters:
      - name: years-json
        valueFrom:
          path: /outputdir/years.json

• Then I want to use year and prev-year in my workflow template. It's possible to do it using loop mechanism by doing something like above

        - name: select-features
          template: t-select-features
          withParam: "{{steps.get-prev-year.outputs.parameters.years-json}}"
          arguments:
            parameters:
              - name: year
                value: "{{item.year}}"
              - name: prev-year
                value: "{{item.prev-year}}"

It works but then if I want to use the outputs artefact (like with from: "{{step.select-features.outputs.artifacts.features}}") or parameters (like with withParam: "{{steps.select-features-s2.outputs.parameters.month-json}}") it won't be possible because my template is run in a loop, even if it is a loop of only one iteration.

Instead of running my template in a loop to read the json values I tried to use the builtin function jsonpath without success. I tryed directly value: "{{=jsonpath(steps.get-prev-year.outputs.parameters.years-json, '$.year')}}" and then by passing the json as input {{=jsonpath(inputs.parameters.year-json, '$.year')}}.
I did it based on https://argoproj.github.io/argo-workflows/conditional-artifacts-parameters/#built-in-functions and https://argoproj.github.io/argo-workflows/variables/#examples.

Maybe there is something I missunderstood in the jsonpath syntax or another way to read json value that I didn't found. I'm working with apiVersion: argoproj.io/v1alpha1

[agilgur5]

Instead of running my template in a loop to read the json values I tried to use the builtin function jsonpath without success. I tryed directly value: "{{=jsonpath(steps.get-prev-year.outputs.parameters.years-json, '$.year')}}" and then by passing the json as input {{=jsonpath(inputs.parameters.year-json, '$.year')}}.
I did it based on https://argoproj.github.io/argo-workflows/conditional-artifacts-parameters/#built-in-functions and https://argoproj.github.io/argo-workflows/variables/#examples.

I believe jsonpath should work here. Per the docs you linked though, dashes in expression syntax can only be used with bracket notation. As in:

{{=jsonpath(steps['get-prev-year'].outputs.parameters['years-json'], '$.year')}}
{{=jsonpath(inputs.parameters['year-json'], '$.year')}}

With dashes/hyphens and no bracket notation, you would get a parsing error, per the expression docs.