I've got quite into the power of Spaties [laravel-model-states](https://spatie.be/docs/laravel-model-states/v2/01-introduction) package. I refactored an app a few years ago, and the state pattern and use of classes for states and transitions cleared up so much confusion.

Upgrading to Laravel 9 though I needed to change to spatie models states v2. Which was more involved because the state system changed heavily to use Laravel's casting system.

While not crazy complicated, I had enough states and have used this on several apps, so I made notes for me to follow with each state to avoid having to cycle between different doc pages.

In your state-using model you need to add the casts attribute linking to the abstract state class:

protected $casts = [
        'status' => ProductState::class,
    ];

Take your registered states code from the model:

///from Model
protected function registerStates(): void
    {
 $this->addState('status', ProductState::class)
            ->default(Active::class)
            ->allowTransition(
                [Development::class, Special::class, Active::class, TBD::class],
                Discontinued::class,
                toDiscontinuedTransition::class
            )
            ->allowTransition(
                [Development::class, Special::class, TBD::class, Discontinued::class],
                Active::class
            )
            ->allowTransition(
                [Special::class, Active::class, Discontinued::class],
                TBD::class
            )
            ->allowTransition(
                [Development::class, Active::class, TBD::class, Discontinued::class],
                Special::class
            )
            ->allowTransition(
                [Active::class, Special::class],
                Development::class
            );
}

And move that to your abstract state class:

//In ProductState.php
public static function config(): StateConfig
    {
        return parent::config()
            ->default(Active::class)
            ->allowTransition(
                [Development::class, Special::class, Active::class, TBD::class],
                Discontinued::class,
                toDiscontinuedTransition::class
            )
            ->allowTransition(
                [Development::class, Special::class, TBD::class, Discontinued::class],
                Active::class
            )
            ->allowTransition(
                [Special::class, Active::class, Discontinued::class],
                TBD::class
            )
            ->allowTransition(
                [Development::class, Active::class, TBD::class, Discontinued::class],
                Special::class
            )
            ->allowTransition(
                [Active::class, Special::class],
                Development::class
            );
    }

Transitioning inside states:

In my states I had a lot of $this->model->transitionTo() to change between states. The new system is $this->transitionTo() a quick find and replace across the states folder fixed that.

There's also a couple of changed methods - all my states worked fine in tests, but there were a few places I was passing a field no longer needed that I took out for completeness.

Review the full changed method list here