Processing input and output in Step Functions
Managing state with variables and JSONata
Step Functions recently added variables and JSONata to manage state and transform data.
Learn more in the blog post Simplifying developer experience with variables and JSONata in AWS Step Functions
When a Step Functions execution receives JSON input, it passes that data to the first state in the workflow as input.
With JSONata, you can retrieve state input from $states.input. Your state machine executions also provide that initial input data in the Context object. You can retrieve the original state machine input at any point in your workflow from $states.context.Execution.Input.
When states exit, their output is available to the very next state in your state machine. Your state inputs will pass through as state output by default, unless you modify the state output. For data that you might need in later steps, consider storing it in variables. For more info, see Passing data between states with variables.
QueryLanguage recommendation
For new state machines, we recommend the JSONata query language. In state machines that do not specify a query language, the state machine defaults to JSONPath for backward compatibility. You must opt-in to use JSONata for your state machines or individual states.
Processing input and output with JSONata
With JSONata expressions, you can select and transform data. In the Arguments
field, you can customize the data sent to the action. The result can be transformed into
custom state output in the Output field. You can also store data in variables
in the Assign field. For more info, see Transforming data with JSONata.
The following diagram shows how JSON information moves through a JSONata task state.
Processing input and output with JSONPath
Managing state and transforming data
Learn about Passing data between states with variables and Transforming data with JSONata.
For state machines that use JSONPath, the following fields control the flow of data from
state to state: InputPath, Parameters,
ResultSelector, ResultPath, and OutputPath. Each
JSONPath field can manipulate JSON as it moves through each state in your workflow.
JSONPath fields can use paths to select portions
of the JSON from the input or the result. A path is a string, beginning with $,
that identifies nodes within JSON text. Step Functions paths use JsonPath
The following diagram shows how JSON information moves through a JSONPath task state. The
InputPath selects the parts of the JSON input to pass to the task of the
Task state (for example, an AWS Lambda function). You can adjust the data that
is sent to your action in the Parameters field. Then, with
ResultSelector, you can select portions of the action result to carry forward.
ResultPath then selects the combination of state input and task results to pass
to the output. OutputPath can filter the JSON output to further limit the
information that's passed to the output.
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