4.2. Repository

4.2.1. Zweck

Vermittelt zwischen dem Domain- und Data-Mapping-Layer indem es ein Interface wie für eine Collection implementierung, um auf Domainobjekte zu zugreifen. Das Repository kapselt dabei alle persistierten Objekte und die Operationen auf diesen um eine objektorientierte Sicht auf die Persistenzschicht zu implementieren. Das Repository unterstützt damit die saubere Trennung und eine Abhängigkeit in nur eine Richtung von Domain- und Data-Mapping-Layern.

4.2.2. Beispiele

  • Doctrine 2 ORM: Repository vermittelt zwischen Entity und DBAL und enthält verschiedene Methoden, um Entities zu erhalten
  • Laravel Framework

4.2.3. UML Diagramm

Alt Repository UML Diagram

4.2.4. Code

Du findest den Code auch auf GitHub

Post.php

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<?php

declare(strict_types=1);

namespace DesignPatterns\More\Repository\Domain;

class Post
{
    public static function draft(PostId $id, string $title, string $text): Post
    {
        return new self(
            $id,
            PostStatus::fromString(PostStatus::STATE_DRAFT),
            $title,
            $text
        );
    }

    public static function fromState(array $state): Post
    {
        return new self(
            PostId::fromInt($state['id']),
            PostStatus::fromInt($state['statusId']),
            $state['title'],
            $state['text']
        );
    }

    private function __construct(
        private PostId $id,
        private PostStatus $status,
        private string $title,
        private string $text
    ) {
    }

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

    public function getStatus(): PostStatus
    {
        return $this->status;
    }

    public function getText(): string
    {
        return $this->text;
    }

    public function getTitle(): string
    {
        return $this->title;
    }
}

PostId.php

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<?php

declare(strict_types=1);

namespace DesignPatterns\More\Repository\Domain;

use InvalidArgumentException;

/**
 * This is a perfect example of a value object that is identifiable by it's value alone and
 * is guaranteed to be valid each time an instance is created. Another important property of value objects
 * is immutability.
 *
 * Notice also the use of a named constructor (fromInt) which adds a little context when creating an instance.
 */
class PostId
{
    public static function fromInt(int $id): PostId
    {
        self::ensureIsValid($id);

        return new self($id);
    }

    private function __construct(private int $id)
    {
    }

    public function toInt(): int
    {
        return $this->id;
    }

    private static function ensureIsValid(int $id)
    {
        if ($id <= 0) {
            throw new InvalidArgumentException('Invalid PostId given');
        }
    }
}

PostStatus.php

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<?php

declare(strict_types=1);

namespace DesignPatterns\More\Repository\Domain;

use InvalidArgumentException;

/**
 * Like PostId, this is a value object which holds the value of the current status of a Post. It can be constructed
 * either from a string or int and is able to validate itself. An instance can then be converted back to int or string.
 */
class PostStatus
{
    public const STATE_DRAFT_ID = 1;
    public const STATE_PUBLISHED_ID = 2;

    public const STATE_DRAFT = 'draft';
    public const STATE_PUBLISHED = 'published';

    private static array $validStates = [
        self::STATE_DRAFT_ID => self::STATE_DRAFT,
        self::STATE_PUBLISHED_ID => self::STATE_PUBLISHED,
    ];

    public static function fromInt(int $statusId)
    {
        self::ensureIsValidId($statusId);

        return new self($statusId, self::$validStates[$statusId]);
    }

    public static function fromString(string $status)
    {
        self::ensureIsValidName($status);
        $state = array_search($status, self::$validStates);

        if ($state === false) {
            throw new InvalidArgumentException('Invalid state given!');
        }

        return new self($state, $status);
    }

    private function __construct(private int $id, private string $name)
    {
    }

    public function toInt(): int
    {
        return $this->id;
    }

    /**
     * there is a reason that I avoid using __toString() as it operates outside of the stack in PHP
     * and is therefor not able to operate well with exceptions
     */
    public function toString(): string
    {
        return $this->name;
    }

    private static function ensureIsValidId(int $status)
    {
        if (!in_array($status, array_keys(self::$validStates), true)) {
            throw new InvalidArgumentException('Invalid status id given');
        }
    }


    private static function ensureIsValidName(string $status)
    {
        if (!in_array($status, self::$validStates, true)) {
            throw new InvalidArgumentException('Invalid status name given');
        }
    }
}

PostRepository.php

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<?php

declare(strict_types=1);

namespace DesignPatterns\More\Repository;

use OutOfBoundsException;
use DesignPatterns\More\Repository\Domain\Post;
use DesignPatterns\More\Repository\Domain\PostId;

/**
 * This class is situated between Entity layer (class Post) and access object layer (Persistence).
 *
 * Repository encapsulates the set of objects persisted in a data store and the operations performed over them
 * providing a more object-oriented view of the persistence layer
 *
 * Repository also supports the objective of achieving a clean separation and one-way dependency
 * between the domain and data mapping layers
 */
class PostRepository
{
    public function __construct(private Persistence $persistence)
    {
    }

    public function generateId(): PostId
    {
        return PostId::fromInt($this->persistence->generateId());
    }

    public function findById(PostId $id): Post
    {
        try {
            $arrayData = $this->persistence->retrieve($id->toInt());
        } catch (OutOfBoundsException $e) {
            throw new OutOfBoundsException(sprintf('Post with id %d does not exist', $id->toInt()), 0, $e);
        }

        return Post::fromState($arrayData);
    }

    public function save(Post $post)
    {
        $this->persistence->persist([
            'id' => $post->getId()->toInt(),
            'statusId' => $post->getStatus()->toInt(),
            'text' => $post->getText(),
            'title' => $post->getTitle(),
        ]);
    }
}

Persistence.php

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<?php

declare(strict_types=1);

namespace DesignPatterns\More\Repository;

interface Persistence
{
    public function generateId(): int;

    public function persist(array $data);

    public function retrieve(int $id): array;

    public function delete(int $id);
}

InMemoryPersistence.php

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<?php

declare(strict_types=1);

namespace DesignPatterns\More\Repository;

use OutOfBoundsException;

class InMemoryPersistence implements Persistence
{
    private array $data = [];
    private int $lastId = 0;

    public function generateId(): int
    {
        $this->lastId++;

        return $this->lastId;
    }

    public function persist(array $data)
    {
        $this->data[$this->lastId] = $data;
    }

    public function retrieve(int $id): array
    {
        if (!isset($this->data[$id])) {
            throw new OutOfBoundsException(sprintf('No data found for ID %d', $id));
        }

        return $this->data[$id];
    }

    public function delete(int $id)
    {
        if (!isset($this->data[$id])) {
            throw new OutOfBoundsException(sprintf('No data found for ID %d', $id));
        }

        unset($this->data[$id]);
    }
}

4.2.5. Теst

Tests/PostRepositoryTest.php

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<?php

declare(strict_types=1);

namespace DesignPatterns\More\Repository\Tests;

use OutOfBoundsException;
use DesignPatterns\More\Repository\Domain\PostId;
use DesignPatterns\More\Repository\Domain\PostStatus;
use DesignPatterns\More\Repository\InMemoryPersistence;
use DesignPatterns\More\Repository\Domain\Post;
use DesignPatterns\More\Repository\PostRepository;
use PHPUnit\Framework\TestCase;

class PostRepositoryTest extends TestCase
{
    private PostRepository $repository;

    protected function setUp(): void
    {
        $this->repository = new PostRepository(new InMemoryPersistence());
    }

    public function testCanGenerateId()
    {
        $this->assertEquals(1, $this->repository->generateId()->toInt());
    }

    public function testThrowsExceptionWhenTryingToFindPostWhichDoesNotExist()
    {
        $this->expectException(OutOfBoundsException::class);
        $this->expectExceptionMessage('Post with id 42 does not exist');

        $this->repository->findById(PostId::fromInt(42));
    }

    public function testCanPersistPostDraft()
    {
        $postId = $this->repository->generateId();
        $post = Post::draft($postId, 'Repository Pattern', 'Design Patterns PHP');
        $this->repository->save($post);

        $this->repository->findById($postId);

        $this->assertEquals($postId, $this->repository->findById($postId)->getId());
        $this->assertEquals(PostStatus::STATE_DRAFT, $post->getStatus()->toString());
    }
}