Handle non-persisted sets of domain entities.

Requires PHP 7.1

Through Composer, obviously:

composer require chrisharrison/entity-sets

In domain driven design (DDD), persistence is abstracted from the domain model. I've found that if you're persisting at the level of the aggregate root, it may not make sense to separately persist certain sets of entities. This library models a set of entities without having to worry about a persistence layer.

Implement the provided Entity interface. The interface is the ValueObject interface (see value objects library) with the addition of a getId() method. This method should return an EntityId.

final class Note implements Entity
{
    use CompositeTrait;

    private $id;
    private $content;

    public function __construct(NoteId $id, Content $content)
    {
        $this->id = $id;
        $this->content = $content;
    }

    public function getId(): NoteId
    {
        return $this->id;
    }

    public function getContent(): Content
    {
        return $this->content;
    }

    public static function fromNative($native)
    {
        return new static(
            NoteId::fromNative($native['id']),
            Content::fromNative($native['content'])
        );
    }
}

An EntityId is also a value object with two additional methods:

interface EntityId extends ValueObject
{
    /**
     * @return static
     */
    public static function start();

    /**
     * @return static
     */
    public function next();
}

The start() method should return a new ID at the start of a sequence.

The next() method should return a new instance of the ID with the sequence advanced by one.

There is a provided trait: EntityIdTrait that implements a simple numeric integer sequence.

final class NoteId implements EntityId
{
    use EntityIdTrait;
}

A set of entities should implement the EntitySet interface. There is a provided abstract class that can be used to easily implement this interface: AbstractEntitySet.

final class NoteSet extends AbstractEntitySet implements EntitySet
{
    protected static function entityType(): string
    {
        return Note::class;
    }

    protected static function entityIdType(): string
    {
        return NoteId::class;
    }
}

Because the set determines an entity's identity (ID) it is not possible to directly add entity objects to a set. Instead, a native representation of the entity should be added using the addNative() method.

$nativeNote = [
    'content' => 'This is a note.',
];

$noteSet = new NoteSet;
$noteSet = $noteSet->addNative($nativeNote);

The method will return a new instance of the set with the entity added. The native value will be parsed through the fromNative method of the provided Entity class and the id property will be populated using the EntityId class.

To update an entity, simply pass an entity to the update() method. This will return a new instance of the set with the entity with the corresponding EntityId replaced.

To remove an entity, simple pass an entity to the remove() method. This will return a new instance of the set with the entity with the corresponding EntityId removed.

All entities can be retrieved from the set with set(). Or a single entity with getById().