<?php
class Post
{
private PostId $id;
private PostStatus $status;
private string $title;
private string $text;
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(PostId $id, PostStatus $status, string $title, string $text)
{
$this->id = $id;
$this->status = $status;
$this->text = $text;
$this->title = $title;
}
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;
}
}
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
{
private int $id;
public static function fromInt(int $id): PostId
{
self::ensureIsValid($id);
return new self($id);
}
private function __construct(int $id)
{
$this->id = $id;
}
public function toInt(): int
{
return $this->id;
}
private static function ensureIsValid(int $id)
{
if ($id <= 0) {
throw new InvalidArgumentException('Invalid PostId given');
}
}
}
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
{
const STATE_DRAFT_ID = 1;
const STATE_PUBLISHED_ID = 2;
const STATE_DRAFT = 'draft';
const STATE_PUBLISHED = 'published';
private static array $validStates = [
self::STATE_DRAFT_ID => self::STATE_DRAFT,
self::STATE_PUBLISHED_ID => self::STATE_PUBLISHED,
];
private int $id;
private string $name;
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(int $id, string $name)
{
$this->id = $id;
$this->name = $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');
}
}
}
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
{
private Persistence $persistence;
public function __construct(Persistence $persistence)
{
$this->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(),
]);
}
}
interface Persistence
{
public function generateId(): int;
public function persist(array $data);
public function retrieve(int $id): array;
public function delete(int $id);
}
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]);
}
}
// USAGE
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());
}
}