State Machine

In Sylius, the default approach to managing frequent changes in the system is through the Symfony Workflow, which offers a highly flexible and well-organized solution. However, Sylius also provides the option to use the Winzou State Machine if preferred.

Both options allow you to define a set of states stored on an entity and manage transitions between them. Additionally, each state machine can be configured with callbacks—events triggered during specific transitions—making it easy to customize how your system responds to changes.

States

States of a state machine are defined as constants on the model of an entity that the state machine is controlling.

How to configure states? Let’s see the example from the Checkout state machine.

# CoreBundle/Resources/config/app/workflow/sylius_order_checkout.yaml
framework:
    workflows:
        !php/const Sylius\Component\Core\OrderCheckoutTransitions::GRAPH:
            type: state_machine
            marking_store:
                type: method
                property: checkoutState
            supports:
                - Sylius\Component\Core\Model\OrderInterface
            initial_marking: !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_CART
            places:
                - !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_CART
                - !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_ADDRESSED
                - !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_SHIPPING_SELECTED
                - !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_SHIPPING_SKIPPED
                - !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_PAYMENT_SELECTED
                - !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_PAYMENT_SKIPPED
                - !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_COMPLETED

# CoreBundle/Resources/config/app/state_machine/sylius_order_checkout.yml
winzou_state_machine:
    sylius_order_checkout:
        class: "%sylius.model.order.class%"
        property_path: checkoutState
        graph: sylius_order_checkout
        state_machine_class: "%sylius.state_machine.class%"
        states:
            cart: ~
            addressed: ~
            shipping_selected: ~
            shipping_skipped: ~
            payment_skipped: ~
            payment_selected: ~
            completed: ~

Transitions

On the graph it would be the connection between two states, defining that you can move from one state to another subsequently.

How to configure transitions? Let’s see the example of our Checkout state machine. Having states configured we can have a transition between the cart state to the addressed state.

# CoreBundle/Resources/config/app/workflow/sylius_order_checkout.yaml
framework:
    workflows:
        !php/const Sylius\Component\Core\OrderCheckoutTransitions::GRAPH:            
            transitions:
                !php/const Sylius\Component\Core\OrderCheckoutTransitions::TRANSITION_ADDRESS:
                    from: 
                        - !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_CART
                        - !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_ADDRESSED
                        - !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_SHIPPING_SELECTED
                        - !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_SHIPPING_SKIPPED
                        - !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_PAYMENT_SELECTED
                        - !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_PAYMENT_SKIPPED
                    to: !php/const Sylius\Component\Core\OrderCheckoutStates::STATE_ADDRESSED

# CoreBundle/Resources/config/app/state_machine/sylius_order_checkout.yml
winzou_state_machine:
    sylius_order_checkout:
        transitions:
            address:
                from: [cart, addressed, shipping_selected, shipping_skipped, payment_selected, payment_skipped]  # here you specify which state is the initial
                to: addressed

Listeners / Callbacks

Listeners can be used to execute actions in reaction to a given transition in Symfony Workflow.

How do you configure Listeners attached to events in Symfony Workflow?

You need to create a Listener that will be waiting for the chosen transition and will invoke the desired behaviors. Below you can see the ProcessCartListner configured for the order_checkout state machine's transitions.

/** src/Sylius/Bundle/CoreBundle/EventListener/Workflow/OrderCheckout/ProcessCartListener.php **/
<?php

declare(strict_types=1);

namespace Sylius\Bundle\CoreBundle\EventListener\Workflow\OrderCheckout;

use Sylius\Component\Core\Model\OrderInterface;
use Sylius\Component\Order\Processor\OrderProcessorInterface;
use Symfony\Component\Workflow\Event\CompletedEvent;
use Webmozart\Assert\Assert;

final class ProcessCartListener
{
    public function __construct(private OrderProcessorInterface $orderProcessor)
    {
    }

    public function __invoke(CompletedEvent $event): void
    {
        /** @var OrderInterface $order */
        $order = $event->getSubject();
        Assert::isInstanceOf($order, OrderInterface::class);

        $this->orderProcessor->process($order);
    }
}
[...]

<!-- src/Sylius/Bundle/CoreBundle/Resources/config/services/listeners/workflow/order_checkout.xml -->
<?xml version="1.0" encoding="UTF-8"?>

<container xmlns="http://symfony.com/schema/dic/services" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">
    <services>
        <defaults public="false" />

        <service id="Sylius\Bundle\CoreBundle\EventListener\Workflow\OrderCheckout\ProcessCartListener">
            <argument type="service" id="sylius.order_processing.order_processor" />
            <tag name="kernel.event_listener" event="workflow.sylius_order_checkout.completed.address" priority="-200"/>
            <tag name="kernel.event_listener" event="workflow.sylius_order_checkout.completed.select_shipping"  priority="-200"/>
            <tag name="kernel.event_listener" event="workflow.sylius_order_checkout.completed.skip_shipping" priority="-200"/>
            <tag name="kernel.event_listener" event="workflow.sylius_order_checkout.completed.select_payment" priority="-200"/>
            <tag name="kernel.event_listener" event="workflow.sylius_order_checkout.completed.skip_payment" priority="-200"/>
        </service>
[...]

Callbacks in Winzou State Machine are used to execute some code before or after applying transitions. Winzou StateMachineBundle adds the ability to use Symfony services in the callbacks.

How do you configure callbacks in Winzou State Machine?

Having a configured transition, you can attach a callback to it before or after. A callback is simply a method of a service you want to be executed.

Below you can see how the sylius_process_cart callback is configured on the sylius_order_checkout state machine.

# CoreBundle/Resources/config/app/state_machine/sylius_order_checkout.yml
winzou_state_machine:
     sylius_order_checkout:
          callbacks:
               # callbacks may be called before or after specified transitions, in the checkout state machine we've got callbacks only after transitions
               after:
                    sylius_process_cart:
                        on: ["select_shipping", "address", "select_payment", "skip_shipping", "skip_payment"]
                        do: ["@sylius.order_processing.order_processor", "process"]
                        args: ["object"]
                        priority: -200

Configuration

In order to use a state machine, you have to define a graph beforehand. A graph is a definition of states, transitions, and optionally callbacks - all attached to an object from your domain. Multiple graphs may be attached to the same object.

In Sylius the best example of a state machine is the one from checkout. It has seven states available: cart, addressed, shipping_selected, shipping_skipped, payment_skipped, payment_selected and completed - which can be achieved by applying some transitions to the entity. For example, when selecting a shipping method during the shipping step of checkout we should apply the select_shipping transition, and after that the state would become shipping_selected.

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