Loop step

The Loop step runs the steps nested under it once for each item in a list. Use it to send each order, line or product to another system one at a time.

Set it up

In the app	`data` field	What it does
Variable to iterate	`variable_to_iterate`	The name of the variable holding the list, like `orders`. An array, or an object (one pass per key).
Index variable	`index_variable`	Optional. Gets the position (or key) on each pass, like `i`.
Data variable	`data_variable`	Gets the current item on each pass, like `order`.

Drag the steps that should run for each item under the Loop.

Declare the index and data variables before the loop, for example $.i = 0; $.order = null; in a Script step, or as job variables, so they're filled in on each pass.

How it behaves

It needs a real list. A variable holding JSON text (like a response body or $.default) fails with variable must be an array or an object, so parse it in a Script step first. A variable that isn't set at all just skips the loop.
An empty list does nothing. The nested steps simply don't run, so you don't need an If Condition just to guard against an empty list. Add one if you want to do something else when there's nothing to process.
There's a limit of 10,000 passes per job, across all Loops in the job. Past that, the job fails with loop iteration limit exceeded: at most 10000 loop iterations per job.
Steps inside a Loop run again on a retry. If the job fails halfway through and is retried, the loop starts again from the first item. Make the calls inside it safe to repeat, for example with an "update if it exists" call or the other system's de-duplication key.

For very large lists, it's often better to send them in one call (or one file) than one call per item. See Transform Data and File.

Example 1: Post an adjustment for each open order

Trigger: Scheduled.

REST Request: Get open orders, Response variable orders_res, Fail on bad response code on.

Script: Read the order list

$.orders = JSON.parse($.orders_res.body) || [];
$.i = 0;
$.order = null;

If Condition: If there are orders, Condition $.orders.length > 0. This one is optional, because a Loop over an empty list does nothing.
Loop: For each order, Variable to iterate orders, Index variable i, Data variable order. Nested under it:
1. Script: Shape the line: $.adjust_body = JSON.stringify({ sku: $.order.sku, quantity: -$.order.quantity });
2. API Request: Post the adjustment, Body {{ adjust_body }}.

Example 2: Send each sale line to another system

Trigger: System Hook, Create Sale.

Script: Read the sale

var sale = JSON.parse($.default);
$.sale = sale;
$.lines = sale.lines || [];
$.line_index = 0;
$.line = null;

If Condition: If the sale has lines (optional, as above).
Loop: For each line, Variable to iterate lines, Index variable line_index, Data variable line. Nested under it:
1. Script: Read the line: $.line_body = JSON.stringify({ sale_id: $.sale.id, item_id: $.line.item_id, quantity: $.line.quantity });
2. REST Request: Send the line, Body {{ line_body }}.

Tips

Use Liquid inside the loop too. {{ line.item_id }} works in the nested steps' fields.
Filter before you loop. A Transform Data step can drop the items you don't need, so the loop does less.

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