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Configure output using the ResultSelector, ResultPath, and OutputPath filters

When the check-address Lambda function is invoked in the WorkflowInputOutput state machine, the function returns an output payload after performing the address verification. On the Execution Details page, choose the Verify address step and view the output payload inside Task result on the Step details pane.

{
    "ExecutedVersion": "$LATEST",
    "Payload": {
      "statusCode": 200,
      "body": "{\"approved\":true,\"message\":\"identity validation passed\"}"
    },
    "SdkHttpMetadata": {
      "AllHttpHeaders": {
        "X-Amz-Executed-Version": [
          "$LATEST"
        ],
        ...
        ...
    "StatusCode": 200
  }

Using ResultSelector

Now if you need to provide the result of the identity and address verification checks to the following states in your workflow, you can select the Payload.body node in the output JSON and use the StringToJson intrinsic function in the ResultSelector filter to format the data as required.

ResultSelector selects what is needed from the task output. In the following example, ResultSelector takes the string in $.Payload.body and applies the States.StringToJson intrinsic function to convert the string to JSON and puts the resulting JSON inside the identity node.

"ResultSelector": {
    "identity.$": "States.StringToJson($.Payload.body)"
  }

Consequently, the following JSON data is created.

{
    "identity": {
      "approved": true,
      "message": "Identity validation passed"
    }
  }

As you work with these input and output filters, you can also encounter runtime errors arising because of specifying invalid JSON path expressions. For more information, see.

Using ResultPath

You can specify a location in the initial input payload to save a state’s task processing result using the ResultPath field. If you don't specify ResultPath, its value defaults to $, which causes the initial input payload to be replaced with the raw task result. If you specify ResultPath as null, the raw result is discarded and the initial input payload becomes the effective output.

If you apply the ResultPath field on the JSON data created using the ResultSelector field, the task result is added inside the results node in the input payload as shown in the following example:

{
  "data": {
    "firstname": "Jane",
    "lastname": "Doe",
    "identity": {
      "email": "jdoe@example.com",
      "ssn": "123-45-6789"
    },
    "address": {
      "street": "123 Main St",
      "city": "Columbus",
      "state": "OH",
      "zip": "43219"
    },
  "results": {
    "identity": {
      "approved": true
    }
  }
}

Using OutputPath

You can select a portion of the state output after the application of ResultPath to pass to the next state. This enables you to filter out unwanted information, and pass only the portion of JSON that you care about.

In the following example, the OutputPath field saves the state output inside the results node: "OutputPath": "$.results". Consequently, the final output of the state, which you can pass to the next state is as follows:

{
    "addressResult": {
      "approved": true,
      "message": "address validation passed"
    },
    "identityResult": {
      "approved": true,
      "message": "identity validation passed"
    }
}

Using console features to visualize the input and output data flows

You can visualize the input and output data flow between the states in your workflows using the Step Functions console’s Data flow simulator or Advanced view option in the Execution Details page.