AWS Map State Input Management

Question

I'm currently making some tests using AWS step functions, despite its ease of use I am not able to correctly manage the input of the map state:

Here is the input provided:

{
"keep": "elementToKeep",
  "my_array": [
    "element0",
    "element1",
    "element2"
  ]
}

I' like to make the map state iterate over my_array such that the inner state recives as input

{ "keep": "elementToKeep", "element": "element0" } at the 1st iteration
{ "keep": "elementToKeep", "element": "element1" } at the 2nd iteration
and so on ...

Right now I am only able to provide "element0" (at the 1st interaction) as input, not even being able to correctly format it with JSONSyntax.

Below I paste the State Machine JSON structure. I am more familiar with the workflow view, but any help is highly appreciated.

{
  "StartAt": "Map",
  "States": {
    "Map": {
      "Type": "Map",
      "End": true,
      "Iterator": {
        "StartAt": "Pass",
        "States": {
          "Pass": {
            "Type": "Pass",
            "End": true
          }
        }
      },
      "ItemsPath": "$.my_array"
    }
  }
}

score 1 · Answer 1 · answered Jul 27 '22 at 12:47

I wasn't able to find what "Transform array items" field is (maybe the name changed), so I ended up on another question with a more detailed answer. I paste it here in case it is useful for others: Pass multiple inputs into Map State in AWS Step Function

"ItemsPath": "$.my_array",
"Parameters": {
  "element.$": "$$.Map.Item.Value",
  "keep.$": "$.keep"
}

score 0 · Accepted Answer · answered Aug 30 '21 at 17:32

After a few hours of digging I found the solution:
For some reason the item of the array provided as input to the inner function (here element0, element1, etc...) is mapped as $$.Map.Item.Value (for some reasons).
So if it's necessary to provide other parameters beside the array element, in the "Transform array items" field is sufficient to place:

{
  "element.$": "$$.Map.Item.Value",
  "keep.$": "$.keep"
}

Which produced the input desired as specified in the question, thus I'll mark the question as closed.

In this link it's possible to find the source for this answer.

AWS Map State Input Management

2 Answers2