Adjusters Pro

Adjuster classes return models that modify pricing when an order is recalculated.

# Writing an Adjuster

Each class implements the Adjuster Interface (opens new window) with an adjust() method for evaluating the order and returning zero or more OrderAdjustment (opens new window) models. Each of those models may be applied to the order or one of its line items.

Do you need your own adjuster?

The built-in adjusters each include integration points that could reduce the amount of custom code you need to write. Look at the existing Discount (opens new window), Shipping (opens new window), and Tax (opens new window) adjusters before you write your own from scratch.

An adjustment model should have a type of shipping, discount, or tax. (Adjustments are applied in that order under the hood.) While it’s technically possible to designate any type value, using one of those three will ensure the adjustment is properly represented to the payment gateway.

The rest of this page covers discount and shipping adjusters even though there is also a tax adjuster type. Only one tax adjuster is allowed, but tax adjustments are deeply customizable via tax engines.

Adjuster models previously allowed setting the type property to any string. This been deprecated and only the type values above will be allowed in Commerce 4.

# Registering a New Adjuster

You can register your adjuster class by including it in the types array attribute of the registerOrderAdjusters or registerDiscountAdjusters event model.

use craft\commerce\services\OrderAdjustments;
use yii\base\Event;
use MyAdjuster;

Event::on(
    OrderAdjustments::class,
    OrderAdjustments::EVENT_REGISTER_ORDER_ADJUSTERS,
    function(RegisterComponentTypesEvent $event) {
        $event->types[] = MyAdjuster::class;
    }
);

The order of the adjustments within the types array is important because adjusters will be called in exactly that sequence when an order is calculated.

Even if you don’t add or replace an adjuster you might still use either event solely to change the order in which existing adjustments are applied.

# Replacing an Adjuster

Because the adjusters are exposed in an array, you could also swap your own custom adjuster for one that’s included. Here, we’re swapping a custom MyShippingAdjuster in place of the included Shipping (opens new window) class:

use craft\commerce\services\OrderAdjustments;
use yii\base\Event;
use craft\commerce\adjusters\Shipping;
use MyShippingAdjuster;

Event::on(
    OrderAdjustments::class,
    OrderAdjustments::EVENT_REGISTER_ORDER_ADJUSTERS,
    function(RegisterComponentTypesEvent $event) {
        $adjusters = $event->types;

        foreach ($adjusters as $key => $adjuster) {
            if ($adjuster == Shipping::class) {
                $adjusters[$key] = MyShippingAdjuster::class;
            }
        }

        $event->types = $adjusters;
    }
);

# Creating Adjustments

The adjuster interface consists of a single method: adjust(Order $order).

Each OrderAdjustment (opens new window) model returned by that adjust method—if it returns any at all—will have adjustment details and should include contextual information that explains why the adjuster returned it:

  • $type should be shipping, discount, or tax to reflect the kind of adjustment.
  • $amount is the value (positive or negative) used to modify the order or line item. (Negative amounts reduce the price of the order.)
  • $orderId is the ID of the applicable order, which should be set via the setOrder() method.
  • $sourceSnapshot is a required array or JSON string that should illuminate the rationale behind the adjustment. The included shipping adjuster, for example, includes whatever matching shipping rules were used to calculate the shipping cost.
  • $lineItemId refers to the ID of an applicable line item on the order, which should optionally be set via the setLineItem() method.
  • $included is false by default, and when true prevents the adjustment from changing the order’s total in order to clarify that it was already included in the price of the order. (The only included adjustment Commerce ships with is used for taxes.)
  • $name is an optional short, human-friendly label for the adjustment.
  • $description is an optional longer, human-friendly description of the adjustment.

# Designating an Order and Line Item

An adjustment model always belongs to an order, but can optionally belong to a line item.

To specify the adjustment’s order, use the setOrder() method when creating the adjustment:

$adjustment->setOrder($order);

To the adjustment’s line item, use the setLineItem() method when creating the adjustment model:

$adjustment->setLineItem($lineItem);

Using these methods ensures the correct order and line item will be referenced even if either one is new and doesn’t yet have an ID.

# Example

Below is an example adjuster class that puts a $2 discount on each line item:

<?php

use craft\base\Component;
use craft\commerce\base\AdjusterInterface;
use craft\commerce\elements\Order;
use craft\commerce\models\OrderAdjustment;

class MyAdjuster extends Component implements AdjusterInterface
{
    public function adjust(Order $order): array
    {
        $adjustments = [];

        foreach ($order->getLineItems() as $item) {
            $adjustment = new OrderAdjustment;
            $adjustment->type = 'discount';
            $adjustment->name = '$2 off';
            $adjustment->description = '$2 off everything in the store';
            // `sourceSnapshot` can contain information to explain the adjustment
            $adjustment->sourceSnapshot = [ 'data' => 'value' ];
            $adjustment->amount = -2;
            $adjustment->setOrder($order);
            $adjustment->setLineItem($item);

            $adjustments[] = $adjustment;
        }

        return $adjustments;
    }
}