Referencing flow variables in custom scripts

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Introduction

If required, you can reference (and therefore manipulate) flow variables in custom scripts. The possibilities here are only as limited as your development expertise however, a simple example might be where you want to generate a running count of order lines, to be output to a total field in a target system.

To achieve this, you would:

1. Add a flow variable named running_total to your process flow settings.
2. Write a custom script which loops over each received order line and updates the running_total variable as it goes.
3. Add the custom script to your process flow via a script shape.
4. Add a map shape to your process flow and include a rule which maps a custom string transform for , to the total field in the target system.

Flow variable syntax for custom scripts

To reference flow variables in a custom script, the required syntax is as follows:

{% code title="PHP 8.1" lineNumbers="true" %}

['flow']['variables']['variableName']

{% code title="Javascript Node 18" lineNumbers="true" %}

flow.variables.variableName

{% code title="C# 8" lineNumbers="true" %}

["flow"]["variables"]["variableName"]

{% code title="Python 3" lineNumbers="true" %}

['flow']['variables']['variableName']

{% code title="Ruby 3" lineNumbers="true" %}

['flow']['variables']['variableName']

In all cases, the variableName element should be replaced with the actual flow variable name. For example:

{% code title="PHP 8.1" lineNumbers="true" %}

['flow']['variables']['running_total']

Example

The example script below takes a flow variable named customerID and sets the value to 1234567:

{% code title="PHP 8.1" lineNumbers="true" %}

<?php

/**
 * Handler function.
 *
 * @param array $data [
 *      'payload'   => (string|null) the payload as a string|null
 *      'variables' => (array[string]string) any variables as key/value
 *      'meta'      => (array[string]string) any meta as key/value
 *    ]
 */

function handle($data)
{
    $data['flow']['variables']['customerID'] = 1234567;

    return $data;
}

So, wherever the customerID flow variable is referenced in a process flow, its value would be set to 1234567 when the process flow runs.

When you update flow variables via a script, those updates persist for the duration of the flow run. Once the process flow has completed, default values are restored.