Writing your first reactor | laravel-event-sourcing | Spatie

 SPATIE

  Laravel Event Sourcing
=========================

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  [Docs](https://spatie.be/docs)  [Laravel-event-sourcing](https://spatie.be/docs/laravel-event-sourcing/v7)  Using-reactors  Writing your first reactor

 Version   v7   v6   v5   v4   v3   v2   v1

 Other versions for crawler [v7](https://spatie.be/docs/laravel-event-sourcing/v7) [v6](https://spatie.be/docs/laravel-event-sourcing/v6) [v5](https://spatie.be/docs/laravel-event-sourcing/v5) [v4](https://spatie.be/docs/laravel-event-sourcing/v4) [v3](https://spatie.be/docs/laravel-event-sourcing/v3) [v2](https://spatie.be/docs/laravel-event-sourcing/v2) [v1](https://spatie.be/docs/laravel-event-sourcing/v1)

- [ Introduction ](https://spatie.be/docs/laravel-event-sourcing/v7/introduction)
- [ Support us ](https://spatie.be/docs/laravel-event-sourcing/v7/support-us)
- [ Requirements ](https://spatie.be/docs/laravel-event-sourcing/v7/requirements)
- [ Installation & setup ](https://spatie.be/docs/laravel-event-sourcing/v7/installation-setup)
- [ Questions and issues ](https://spatie.be/docs/laravel-event-sourcing/v7/questions-issues)
- [ Changelog ](https://spatie.be/docs/laravel-event-sourcing/v7/changelog)
- [ Upgrading ](https://spatie.be/docs/laravel-event-sourcing/v7/upgrading)
- [ Resources and alternatives ](https://spatie.be/docs/laravel-event-sourcing/v7/resources-and-alternatives)
- [ About us ](https://spatie.be/docs/laravel-event-sourcing/v7/about-us)

Getting familiar with event sourcing
------------------------------------

- [ Introduction ](https://spatie.be/docs/laravel-event-sourcing/v7/getting-familiar-with-event-sourcing/introduction)
- [ The traditional application ](https://spatie.be/docs/laravel-event-sourcing/v7/getting-familiar-with-event-sourcing/the-traditional-application)
- [ Using projectors to transform events ](https://spatie.be/docs/laravel-event-sourcing/v7/getting-familiar-with-event-sourcing/using-projectors-to-transform-events)
- [ Using aggregates to make decisions based on the past ](https://spatie.be/docs/laravel-event-sourcing/v7/getting-familiar-with-event-sourcing/using-aggregates-to-make-decisions-based-on-the-past)

Using projectors
----------------

- [ Writing your first projector ](https://spatie.be/docs/laravel-event-sourcing/v7/using-projectors/writing-your-first-projector)
- [ Creating and registering projectors ](https://spatie.be/docs/laravel-event-sourcing/v7/using-projectors/creating-and-configuring-projectors)
- [ Making sure events get handled in the right order ](https://spatie.be/docs/laravel-event-sourcing/v7/using-projectors/making-sure-events-get-handled-in-the-right-order)
- [ Thinking in events ](https://spatie.be/docs/laravel-event-sourcing/v7/using-projectors/thinking-in-events)

Using reactors
--------------

- [ Writing your first reactor ](https://spatie.be/docs/laravel-event-sourcing/v7/using-reactors/writing-your-first-reactor)
- [ Creating and configuring reactors ](https://spatie.be/docs/laravel-event-sourcing/v7/using-reactors/creating-and-configuring-reactors)

Using aggregates
----------------

- [ Writing your first aggregate ](https://spatie.be/docs/laravel-event-sourcing/v7/using-aggregates/writing-your-first-aggregate)
- [ Creating and configuring aggregates ](https://spatie.be/docs/laravel-event-sourcing/v7/using-aggregates/creating-and-configuring-aggregates)
- [ Testing aggregates ](https://spatie.be/docs/laravel-event-sourcing/v7/using-aggregates/testing-aggregates)
- [ Snapshots ](https://spatie.be/docs/laravel-event-sourcing/v7/using-aggregates/snapshots)

Advanced usage
--------------

- [ Preparing events ](https://spatie.be/docs/laravel-event-sourcing/v7/advanced-usage/preparing-events)
- [ Replaying events ](https://spatie.be/docs/laravel-event-sourcing/v7/advanced-usage/replaying-events)
- [ Storing metadata ](https://spatie.be/docs/laravel-event-sourcing/v7/advanced-usage/storing-metadata)
- [ Handling exceptions ](https://spatie.be/docs/laravel-event-sourcing/v7/advanced-usage/handling-exceptions)
- [ Discovering projectors and reactors ](https://spatie.be/docs/laravel-event-sourcing/v7/advanced-usage/discovering-projectors-and-reactors)
- [ Using your own event storage model ](https://spatie.be/docs/laravel-event-sourcing/v7/advanced-usage/using-your-own-event-storage-model)
- [ Using your own event storage repository ](https://spatie.be/docs/laravel-event-sourcing/v7/advanced-usage/using-your-own-event-storage-repository)
- [ Using your own event serializer ](https://spatie.be/docs/laravel-event-sourcing/v7/advanced-usage/using-your-own-event-serializer)
- [ Using aliases for stored event classes ](https://spatie.be/docs/laravel-event-sourcing/v7/advanced-usage/using-aliases-for-stored-event-classes)
- [ Adding and Removing Projectors and Reactors ](https://spatie.be/docs/laravel-event-sourcing/v7/advanced-usage/adding-and-removing-projectors-and-reactors)
- [ Aggregate Partials ](https://spatie.be/docs/laravel-event-sourcing/v7/advanced-usage/aggregate-partials)
- [ Event Queries ](https://spatie.be/docs/laravel-event-sourcing/v7/advanced-usage/event-queries)
- [ Commands ](https://spatie.be/docs/laravel-event-sourcing/v7/advanced-usage/commands)

 Writing your first reactor
==========================

###  On this page

1. [ What is a reactor ](#content-what-is-a-reactor)
2. [ Creating your first reactor ](#content-creating-your-first-reactor)
3. [ Using the reactor ](#content-using-the-reactor)
4. [ Want to know more? ](#content-want-to-know-more)

What is a reactor
-----------------------------------------------------------------------------------------------------------

Now that you've [written your first projector](/docs/laravel-event-sourcing/v7/using-projectors/writing-your-first-projector), let's learn how to handle side effects. With side effects we mean things like sending a mail, sending a notification, ... You only want to perform these actions when the original event happens. You don't want to do this work when replaying events.

A reactor is a class, that much like a projector, listens for incoming events. Unlike projectors however, reactors will not get called when events are replayed. Reactors only will get called when the original event fires.

Reactors that perform some kind of API calls, think sending a mail or a notification, will be slow. We highly recommend that all reactors implement `Illuminate\Contracts\Queue\ShouldQueue`. Letting your reactor implement this marker interface will make the package start a queue job. The reactor will be called when that queued job is handled.

Creating your first reactor
-----------------------------------------------------------------------------------------------------------------------------------------

Let's create your first reactor. You can perform `php artisan make:reactor BigAmountAddedReactor` to create a reactor in `app\Reactors`. We will make this reactor send a mail to the director of the bank whenever a big amount of money is added to an account. Typehinting `MoneyAdded` will make our package call `onMoneyAdded` when the event occurs.

```
namespace App\Reactors;

use App\Account;
use App\Events\MoneyAdded;
use App\Mail\BigAmountAddedMail;
use Illuminate\Contracts\Queue\ShouldQueue;
use Illuminate\Support\Facades\Mail;
use Spatie\EventSourcing\EventHandlers\Reactors\Reactor;

class BigAmountAddedReactor extends Reactor implements ShouldQueue
{
    public function onMoneyAdded(MoneyAdded $event)
    {
        if ($event->amount < 900) {
            return;
        }

        $account = Account::uuid($event->accountUuid);

        Mail::to('director@bank.com')->send(new BigAmountAddedMail($account, $event->amount));
    }
}
```

By default, the package will automatically find and use your reactor.

Using the reactor
-----------------------------------------------------------------------------------------------------------

The reactor above will send an email to the director of the bank whenever an amount of 900 or more gets added to an account. Let's put the reactor to work.

```
$account = Account::createWithAttributes(['name' => 'Rey']);
$account->addMoney(1000);
```

A mail will be sent to the director.

If you truncate the `accounts` table and rebuild the contents with

```
php artisan event-sourcing:replay
```

no mail will be sent.

Want to know more?
------------------------------------------------------------------------------------------------------------

Reactors and process managers (which are built on top of the core reactor principle) are thoroughly discussed in [Event Sourcing in Laravel](https://event-sourcing-laravel.com/). More specifically, you want to read these chapters:

- 8. Reactors
- 15. Sagas