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AWS Documentation » AWS Step Functions » Developer Guide » How Step Functions Works » Input and Output Processing in Step Functions » InputPath and Parameters

InputPath and Parameters

Both the "InputPath" and "Parameters" fields provide a way to manipulate JSON as it moves through your workflow. InputPath can limit the input that is passed by filtering the JSON notation by using a path (see Paths). The "Parameters" field enables you to pass a collection of key-value pairs, where the values are either static values that you define in your state machine definition, or that are selected from the input using a path.

AWS Step Functions applies the "InputPath" field first, and then the "Parameters" field. You can first filter your raw input to a selection you want using InputPath, and then apply Parameters to manipulate that input further, or add new values.

InputPath

Use InputPath to select a portion of the state input.

For example, suppose the input to your state includes the following.

{
  "comment": "Example for InputPath.",
  "dataset1": {
    "val1": 1,
    "val2": 2,
    "val3": 3
  },
  "dataset2": {
    "val1": "a",
    "val2": "b",
    "val3": "c"
  }
}

You could apply the InputPath. 

"InputPath": "$.dataset2",

With the previous InputPath, the following is the JSON that is passed as the input. 

{
  "val1": "a",
  "val2": "b",
  "val3": "c"
}

Note

A path can yield a selection of values. Consider the following example.

{ "a": [1, 2, 3, 4] }

If you apply the path $.a[0:2], the following is the result. 

[ 1, 2 ]

Parameters

Use "Parameters" field to create a collection of key-value pairs that are passed as input. The values of each can either be static values that you include in your state machine definition, or selected from either the input or the context object with a path. For key-value pairs where the value is selected using a path, the key name must end in .$.

For example, suppose you provide the following input. 

{
  "comment": "Example for Parameters.",
  "product": {
    "details": {
       "color": "blue",
       "size": "small",
       "material": "cotton"
    },
    "availability": "in stock",
    "sku": "2317",
    "cost": "$23"
  }
}

To select some of the information, you could specify these parameters in your state machine definition. 

"Parameters": {
        "comment": "Selecting what I care about.",
        "MyDetails": {
          "size.$": "$.product.details.size",
          "exists.$": "$.product.availability",
          "StaticValue": "foo"
        }
      },

Given the previous input and the "Parameters" field, this is the JSON that is passed. 

{
  "comment": "Selecting what I care about.",
  "MyDetails": {
      "size": "small",
      "exists": "in stock",
      "StaticValue": "foo"
  }
},

In addition to the input, you can access a special JSON object, known as the context object. The context object includes information about your state machine execution. See The Context Object.

Note

The "Parameters" field can also pass information to connected resources. For example, if your task state is orchestrating an AWS Batch job, you can pass the relevant API parameters directly to the API actions of that service. For more information, see:

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