Aggregate Partials | laravel-event-sourcing | Spatie

 SPATIE

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

spatie.be/open-source

  [Docs](https://spatie.be/docs)  [Laravel-event-sourcing](https://spatie.be/docs/laravel-event-sourcing/v7)  Advanced-usage  Aggregate Partials

 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)

 Aggregate Partials
==================

###  On this page

1. [ Want to know more? ](#content-want-to-know-more)

Aggregate partials can be used to split large aggregate roots into separate classes. An aggregate partial belongs to an aggregate root, so from the outside you'd still interact with the aggregate root.

Just like aggregate roots, aggregate partials can record and apply events, these events are linked to the aggregate root a partial belongs to.

Here's an example of an aggregate partial, which manages cart items and is part of the cart aggregate root:

```
namespace Spatie\Shop\Cart\Partials;

use Spatie\EventSourcing\AggregateRoots\AggregatePartial;

class CartItems extends AggregatePartial
{
    private array $cartItems = [];

    public function isEmpty(): bool
    {
        return count($this->cartItems) === 0;
    }

    public function addItem(
        string $cartItemUuid,
        Product $product,
        int $amount
    ): self {
        $this->recordThat(new CartItemAdded(
            cartItemUuid: $cartItemUuid,
            productUuid: $product->uuid,
            amount: $amount,
        ));

        return $this;
    }

    protected function applyCartItemAdded(
        CartItemAdded $cartItemAdded
    ): void {
        $this->cartItems[$cartItemAdded->cartItemUuid] = null;
    }
}
```

The cart aggregate root, in its turn, links to its partials by adding them as protected properties:

```
class CartAggregateRoot extends AggregateRoot
{
    protected CartItems $cartItems;

    public function __construct()
    {
        $this->cartItems = new CartItems($this);
    }
}
```

The package will determine automatically that `CartItems` is a partial, and will dispatch events to it without any other configuration.

As said before, you'd still interact with the aggregate root from the outside, so `CartAggregateRoot` still needs a method to add an item, though all functionality related to it is moved to a separate class:

```
class CartAggregateRoot extends AggregateRoot
{
    // …

    public function addItem(
        string $cartItemUuid,
        Product $product,
        int $amount
    ): self {
        $this->cartItems->addItem(
            $cartItemUuid,
            $product,
            $amount,
        );

        return $this;
    }
}
```

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

Our course, [Event Sourcing in Laravel](https://event-sourcing-laravel.com/) covers aggregate roots and partials in depth:

- 9. Aggregate Roots
- 10. State Management in Aggregate Roots
- 11. Aggregate Partials
- 12. State Machines with Aggregate Partials