Spatie Laravel Event Sourcing – Event sourcing implementation

Spatie Laravel Event Sourcing is a powerful package that enables event sourcing in your Laravel applications. Event sourcing is a design pattern that stores the state of an application as a sequence of events, rather than as a current state snapshot. This approach can improve scalability, maintainability, and provide a clear audit trail of how data changes over time.

Key Features

Event Storage: Store all changes to your application state as events, providing a complete history of data changes.
Rebuild State: Easily reconstruct the current state of an entity by replaying its events.
Snapshotting: Optimize performance by taking snapshots of the current state, reducing the number of events to replay.
Integration with Laravel: Seamlessly integrates with Laravel’s features and conventions, making it easy to use within existing applications.

Installation

To install the package, you can use Composer:

bash

composer require spatie/laravel-event-sourcing

1	composer require spatie/laravel-event-sourcing

Configuration

After installation, you may publish the configuration file:

bash

php artisan vendor:publish --provider="Spatie\EventSourcing\EventSourcingServiceProvider"

1	php artisan vendor:publish --provider="Spatie\EventSourcing\EventSourcingServiceProvider"

This command will create a configuration file at config/event-sourcing.php, where you can adjust various settings.

Basic Concepts

Events

Events are the core of event sourcing. They represent something that has happened in your application. For example, you might have an event called UserRegistered:

php

namespace App\Events;

use Spatie\EventSourcing\AggregateRoots\AggregateRoot;

class UserRegistered
{
    public string $userId;
    public string $email;

    public function __construct(string $userId, string $email)
    {
        $this->userId = $userId;
        $this->email = $email;
    }
}

namespace App\Events;

use Spatie\EventSourcing\AggregateRoots\AggregateRoot;

class UserRegistered

{

public string $userId;

public string $email;

public function __construct(string $userId, string $email)

{

$this->userId = $userId;

$this->email = $email;

}

Aggregate Roots

Aggregate roots are the entry point for working with an aggregate. They contain the logic for applying events and creating new events. For example:

php

namespace App\Aggregates;

use Spatie\EventSourcing\AggregateRoots\AggregateRoot;

class UserAggregate extends AggregateRoot
{
    public function register(string $userId, string $email)
    {
        $this->recordThat(new UserRegistered($userId, $email));
    }
}

namespace App\Aggregates;

use Spatie\EventSourcing\AggregateRoots\AggregateRoot;

class UserAggregate extends AggregateRoot

{

public function register(string $userId, string $email)

{

$this->recordThat(new UserRegistered($userId, $email));

}

Command Handlers

Commands represent an intention to change the state of an aggregate. You typically create command handlers to process these commands:

php

namespace App\Handlers;

use App\Aggregates\UserAggregate;
use App\Commands\RegisterUser;

class RegisterUserHandler
{
    public function __invoke(RegisterUser $command)
    {
        UserAggregate::retrieve($command->userId)->register($command->userId, $command->email);
    }
}

namespace App\Handlers;

use App\Aggregates\UserAggregate;

use App\Commands\RegisterUser;

class RegisterUserHandler

{

public function __invoke(RegisterUser $command)

{

UserAggregate::retrieve($command->userId)->register($command->userId, $command->email);

}

Using Event Sourcing

Define Events: Create event classes to represent the different state changes in your application.
Create Aggregate Roots: Implement aggregate roots to apply events and manage your application’s state.
Define Commands: Create command classes that represent actions users can take that will trigger state changes.
Implement Command Handlers: Write command handlers that process commands and modify the state of your aggregates.
Listen for Events: Use event listeners to respond to the events that occur in your application.

Rebuilding State

To retrieve the current state of an aggregate, you can use the retrieve method:

php

$aggregate = UserAggregate::retrieve($userId);

1	$aggregate = UserAggregate::retrieve($userId);

This will automatically load and replay all events related to that aggregate to reconstruct its current state.

Snapshotting

To improve performance, you can take snapshots of your aggregates, which will allow you to skip replaying earlier events:

php

$aggregate->takeSnapshot();

1	$aggregate->takeSnapshot();

You can configure snapshotting in the package’s configuration file to determine when snapshots should be taken.

Conclusion

Spatie Laravel Event Sourcing provides a robust implementation of event sourcing for Laravel applications, allowing you to manage state changes effectively. By using events to represent state changes, you can maintain a clear history of your application’s data and easily rebuild its current state as needed. This approach improves the maintainability and scalability of your applications.