Question 18859 in Amazon Web Sevices Question posted in
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How to pass parameters from one Pass state to another? – Amazon Web Sevices

How to pass parameters from one Pass state to another?
aws_stepfunctions.JsonPath.string_at is working fine when invoking lambda function (insude aws_stepfunctions.TaskInput.from_object) but it is not working with Pass state (inside aws_stepfunctions.Result.from_object

I have:

initial_pass = aws_stepfunctions.Pass(
    self,
    "initial_pass",
    result=aws_stepfunctions.Result.from_object(
         {
            "iterator": {"count": 5, "index": 0, "step": 1, "continue": True},
            "globals": {
                "start_datetime": "2023-01-01",
                 "end_datetime": "",
                 "upload_start_datetime": "",
                 "upload_end_datetime": "",
                 "device_details": {},
            },
         }
   )
)

second_pass = aws_stepfunctions.Pass(
    self,
    "second_pass",
    result=aws_stepfunctions.Result.from_object(
       {
           "iterator": {"count": 5, "index": 0, "step": 1, "continue": True},
           "globals": aws_stepfunctions.JsonPath.string_at("$.globals"),
       }
    ),
)

I am getting this as output:

{
  "iterator": {
    "count": 5,
    "index": 0,
    "step": 1,
    "continue": true
  },
  "globals": "$.globals"
}
Tags:

2

Answers


  1. 0

    The problem is because the aws_stepfunctions.JsonPath.string_at method returns a string, not an actual value of the referenced path.

    To solve it, try extracting the value of the reference in initial_pass and pass it as a parameter to second_pass.

    Like thiss:

    initial_pass = aws_stepfunctions.Pass(
    self,
    "initial_pass",
    result=aws_stepfunctions.Result.from_object(
         {
            "iterator": {"count": 5, "index": 0, "step": 1, "continue": True},
            "globals": {
                "start_datetime": "2023-01-01",
                 "end_datetime": "",
                 "upload_start_datetime": "",
                 "upload_end_datetime": "",
                 "device_details": {},
            },
         }
   )
)

globals = initial_pass.result["globals"]

second_pass = aws_stepfunctions.Pass(
    self,
    "second_pass",
    result=aws_stepfunctions.Result.from_object(
       {
           "iterator": {"count": 5, "index": 0, "step": 1, "continue": True},
           "globals": globals,
       }
    ),
)

    Edit:

    It seems that the result attribute is not supported in the Pass state of AWS Step Functions.

    As a workaround, you could pass the result of the initial_pass state as input to the second_pass state, and then extract the required fields using JsonPath.

    Delete the line:

    globals = initial_pass.result["globals"]

    Replace second_pass with:

    second_pass = aws_stepfunctions.Pass(
    self,
    "second_pass",
    input_path=aws_stepfunctions.JsonPath.string_at("$.result"),
    result=aws_stepfunctions.Result.from_object(
        {
            "iterator": {"count": 5, "index": 0, "step": 1, "continue": True},
            "globals": aws_stepfunctions.JsonPath.string_at("$.globals"),
        }
    ),
)
    Login or Signup to reply.
  2. 0

    TL;DR Use the parameters arg instead of result.

    The Pass State Result field only accepts static values. It does not perform JSONPath substitutions and does not support intrinsic functions.

    The Parameters field permits transformations. It overrides the preceding state’s input with new key-value pairs. The values can include JSONPath substitutions and intrinsic functions.

    second_pass = aws_stepfunctions.Pass(
    self,
    "second_pass",
    parameters={
        "iterator": {"count": 5, "index": 0, "step": 1, "continue": True},
        "globals": aws_stepfunctions.JsonPath.string_at("$.globals"),
    },
)
    Login or Signup to reply.
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