ItemsPath - AWS Step Functions

ItemsPath

The ItemsPath field is used in a Map state to select an array in the input. A Map state is used to iterate steps for each item in an array contained in the input. By default, a Map state sets ItemsPath to "$" selecting the entire input. If the input to the Map state is a JSON array it will run an iteration for each item in the array, passing that item to the iteration as input. For an example of this, see the Map State Tutorial.

The ItemsPath field allows you to specify a location in the input to find the JSON array to use for iterations. The value of ItemsPath must be a Reference Path, and it must identify a value that is a JSON array. For instance, consider input to a Map state that includes two arrays, like the following example. 

{
  "ThingsPiratesSay": [
    {
      "say": "Avast!"
    },
    {
      "say": "Yar!"
    },
    {
      "say": "Walk the Plank!"
    }
  ],
  "ThingsGiantsSay": [
    {
      "say": "Fee!"
    },
    {
      "say": "Fi!"
    },
    {
      "say": "Fo!"
    },
    {
      "say": "Fum!"
    }
  ]
}

In this case, you could specify which array to use for Map state iterations by selecting a specific array with ItemsPath. The following state machine definition specifies the "ThingsPiratesSay" array in the input using ItemsPath, and will run an iteration of the SayWord pass state for each item in the "ThingsPiratesSay" array. 

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

When processing input, ItemsPath is applied after InputPath. It operates on the effective input to the state, after InputPath has filtered the input.

For more information on Map states, see the following: