Use JSONPath Filter Expression in AWS Step Function with variable in condition

Question

I would like to filter a specific object from an array using a JSONPath filter expression within an AWS Step Function.

The JSONPath expression: $.IncidentRecordSummaries[?(@.Title==$.TitleFilter)].Arn

The data to filter on:

{
  "TitleFilter": "ALARM [hello]",
  "IncidentRecordSummaries": [
    {
      "Arn": "arn:aws:ssm-incidents::12345:incident-record/foo/abc",
      "CreationTime": "2023-02-23T16:54:34.241Z",
      "Impact": 3,
      "IncidentRecordSource": {
        "CreatedBy": "arn:aws:sts::12345:assumed-role/cs-mon-incidents-ms-ac-cloudwatch-sfn/step-functions-express-123",
        "InvokedBy": "states.amazonaws.com",
        "Source": "aws.cloudwatch"
      },
      "Status": "OPEN",
      "Title": "ALARM [hello]"
    },
    {
      "Arn": "arn:aws:ssm-incidents::12345:incident-record/bar/def",
      "CreationTime": "2023-02-23T16:25:51.772Z",
      "Impact": 3,
      "IncidentRecordSource": {
        "CreatedBy": "arn:aws:sts::12345:assumed-role/cs-mon-incidents-ms-pest-devops-guru-sfn/step-functions-express-456",
        "InvokedBy": "states.amazonaws.com",
        "Source": "aws.cloudwatch"
      },
      "Status": "OPEN",
      "Title": "ALARM [world]"
    }
  ]
}

Expected result:

["arn:aws:ssm-incidents::12345:incident-record/foo/abc"`]

Actual result: []

Any suggestion how to solve this issue?

The filter is working with a string literal being used in the expression: $.IncidentRecordSummaries[?(@.Title=='ALARM [hello]')].Arn returns the expected result.

Justin Callison · Accepted Answer · 2023-03-02 20:24:34Z

This form of filter expression should work for Parameters, ResultSelector, InputPath, or OutputPath. See an example below using Pass states and Parameters.

{
  "StartAt": "Generate Input",
  "States": {
    "Generate Input": {
      "Type": "Pass",
      "Result": {
        "TitleFilter": "ALARM [hello]",
        "IncidentRecordSummaries": [
          {
            "Arn": "arn:aws:ssm-incidents::12345:incident-record/foo/abc",
            "CreationTime": "2023-02-23T16:54:34.241Z",
            "Impact": 3,
            "IncidentRecordSource": {
              "CreatedBy": "arn:aws:sts::12345:assumed-role/cs-mon-incidents-ms-ac-cloudwatch-sfn/step-functions-express-123",
              "InvokedBy": "states.amazonaws.com",
              "Source": "aws.cloudwatch"
            },
            "Status": "OPEN",
            "Title": "ALARM [hello]"
          },
          {
            "Arn": "arn:aws:ssm-incidents::12345:incident-record/bar/def",
            "CreationTime": "2023-02-23T16:25:51.772Z",
            "Impact": 3,
            "IncidentRecordSource": {
              "CreatedBy": "arn:aws:sts::12345:assumed-role/cs-mon-incidents-ms-pest-devops-guru-sfn/step-functions-express-456",
              "InvokedBy": "states.amazonaws.com",
              "Source": "aws.cloudwatch"
            },
            "Status": "OPEN",
            "Title": "ALARM [world]"
          }
        ]
      },
      "Next": "Extract Arns"
    },
    "Extract Arns": {
      "Type": "Pass",
      "End": true,
      "Parameters": {
        "key.$": "$.IncidentRecordSummaries[?(@.Title==$.TitleFilter)].Arn"
      }
    }
  }
}

When you run this, you will get the following output:

{
  "key": [
    "arn:aws:ssm-incidents::12345:incident-record/foo/abc"
  ]
}

I wonder if you might be using this in a Task state after calling an API using AWS SDK Service Integrations. In which case, the response you get back is the full API response where the data you want is under the Payload key. In which case you need you need to use $.Payload.IncidentRecordSummaries[?(@.Title==$.Payload.TitleFilter)].Arn instead of $.IncidentRecordSummaries[?(@.Title==$.TitleFilter)].Arn

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