POC: aggregate id

src/Aggregate/AggregateIdNotFound.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\EventSourcing\Aggregate;
+
+use RuntimeException;
+
+use function sprintf;
+
+final class AggregateIdNotFound extends RuntimeException
+{
+    /** @param class-string $className */
+    public function __construct(string $className)
+    {
+        parent::__construct(sprintf('class %s has no property marked as aggregate id', $className));
+    }
+}

src/Aggregate/AggregateRoot.php

@@ -6,7 +6,7 @@
 
 interface AggregateRoot
 {
-    public function aggregateRootId(): string;
+    public function aggregateRootId(): AggregateRootId;
 
     /** @param iterable<object> $events */
     public function catchUp(iterable $events): void;

src/Aggregate/AggregateRootAttributeBehaviour.php

@@ -4,13 +4,17 @@
 
 namespace Patchlevel\EventSourcing\Aggregate;
 
+use ReflectionProperty;
+
 use function array_key_exists;
 
 trait AggregateRootAttributeBehaviour
 {
     use AggregateRootBehaviour;
     use AggregateRootMetadataAwareBehaviour;
 
+    private AggregateRootId|null $_aggregateRootId = null;
+
     protected function apply(object $event): void
     {
         $metadata = static::metadata();
@@ -26,4 +30,24 @@ protected function apply(object $event): void
         $method = $metadata->applyMethods[$event::class];
         $this->$method($event);
     }
+
+    public function aggregateRootId(): AggregateRootId
+    {
+        if ($this->_aggregateRootId instanceof AggregateRootId) {
+            return $this->_aggregateRootId;
+        }
+
+        $metadata = static::metadata();
+
+        $reflection = new ReflectionProperty($this, $metadata->idProperty);
+
+        /** @var mixed $aggregateId */
+        $aggregateId = $reflection->getValue($this);
+
+        if (!$aggregateId instanceof AggregateRootId) {
+            throw new AggregateIdNotFound($this::class);
+        }
+
+        return $this->_aggregateRootId = $aggregateId;
+    }
 }

src/Aggregate/AggregateRootId.php

@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\EventSourcing\Aggregate;
+
+interface AggregateRootId
+{
+    public function toString(): string;
+}

src/Aggregate/BasicAggregateRootId.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\EventSourcing\Aggregate;
+
+final class BasicAggregateRootId implements AggregateRootId
+{
+    public function __construct(
+        private readonly string $id,
+    ) {
+    }
+
+    public function toString(): string
+    {
+        return $this->id;
+    }
+}

src/Attribute/AggregateId.php

@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\EventSourcing\Attribute;
+
+use Attribute;
+
+#[Attribute(Attribute::TARGET_PROPERTY)]
+final class AggregateId
+{
+}

src/Metadata/AggregateRoot/AggregateIdNotFound.php

@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\EventSourcing\Metadata\AggregateRoot;
+
+use RuntimeException;
+
+use function sprintf;
+
+final class AggregateIdNotFound extends RuntimeException
+{
+    public function __construct(string $className)
+    {
+        parent::__construct(sprintf('class %s has no property marked as aggregate id', $className));
+    }
+}

src/Metadata/AggregateRoot/AggregateRootMetadata.php

@@ -13,6 +13,7 @@ public function __construct(
         /** @var class-string<T> */
         public readonly string $className,
         public readonly string $name,
+        public readonly string $idProperty,
         /** @var array<class-string, string> */
         public readonly array $applyMethods,
         /** @var array<class-string, true> */

src/Metadata/AggregateRoot/AttributeAggregateRootMetadataFactory.php

@@ -6,6 +6,7 @@
 
 use Patchlevel\EventSourcing\Aggregate\AggregateRoot;
 use Patchlevel\EventSourcing\Attribute\Aggregate;
+use Patchlevel\EventSourcing\Attribute\AggregateId;
 use Patchlevel\EventSourcing\Attribute\Apply;
 use Patchlevel\EventSourcing\Attribute\Snapshot as AttributeSnapshot;
 use Patchlevel\EventSourcing\Attribute\SuppressMissingApply;
@@ -41,13 +42,15 @@ public function metadata(string $aggregate): AggregateRootMetadata
         $reflector = new ReflectionClass($aggregate);
 
         $aggregateName = $this->findAggregateName($reflector);
+        $idProperty = $this->findIdProperty($reflector);
         [$suppressEvents, $suppressAll] = $this->findSuppressMissingApply($reflector);
         $applyMethods = $this->findApplyMethods($reflector, $aggregate);
         $snapshot = $this->findSnapshot($reflector);
 
         $metadata = new AggregateRootMetadata(
             $aggregate,
             $aggregateName,
+            $idProperty,
             $applyMethods,
             $suppressEvents,
             $suppressAll,
@@ -97,6 +100,23 @@ private function findAggregateName(ReflectionClass $reflector): string
         return $aggregateAttribute->name();
     }
 
+    private function findIdProperty(ReflectionClass $reflector): string
+    {
+        $properties = $reflector->getProperties();
+
+        foreach ($properties as $property) {
+            $attributes = $property->getAttributes(AggregateId::class);
+
+            if ($attributes === []) {
+                continue;
+            }
+
+            return $property->getName();
+        }
+
+        throw new AggregateIdNotFound($reflector->getName());
+    }
+
     private function findSnapshot(ReflectionClass $reflector): Snapshot|null
     {
         $attributeReflectionList = $reflector->getAttributes(AttributeSnapshot::class);

src/Repository/AggregateDetached.php

@@ -5,19 +5,20 @@
 namespace Patchlevel\EventSourcing\Repository;
 
 use Patchlevel\EventSourcing\Aggregate\AggregateRoot;
+use Patchlevel\EventSourcing\Aggregate\AggregateRootId;
 
 use function sprintf;
 
 final class AggregateDetached extends RepositoryException
 {
     /** @param class-string<AggregateRoot> $aggregateClass */
-    public function __construct(string $aggregateClass, string $aggregateId)
+    public function __construct(string $aggregateClass, AggregateRootId $aggregateId)
     {
         parent::__construct(
             sprintf(
                 'An error occurred while saving the aggregate "%s" with the ID "%s", causing the uncommitted events to be lost. Please reload the aggregate.',
                 $aggregateClass,
-                $aggregateId,
+                $aggregateId->toString(),
             ),
         );
     }

src/Repository/AggregateNotFound.php

@@ -4,12 +4,14 @@
 
 namespace Patchlevel\EventSourcing\Repository;
 
+use Patchlevel\EventSourcing\Aggregate\AggregateRootId;
+
 use function sprintf;
 
 final class AggregateNotFound extends RepositoryException
 {
-    public function __construct(string $aggregateClass, string $id)
+    public function __construct(string $aggregateClass, AggregateRootId $id)
     {
-        parent::__construct(sprintf('aggregate "%s::%s" not found', $aggregateClass, $id));
+        parent::__construct(sprintf('aggregate "%s::%s" not found', $aggregateClass, $id->toString()));
     }
 }

src/Repository/AggregateUnknown.php

@@ -5,19 +5,20 @@
 namespace Patchlevel\EventSourcing\Repository;
 
 use Patchlevel\EventSourcing\Aggregate\AggregateRoot;
+use Patchlevel\EventSourcing\Aggregate\AggregateRootId;
 
 use function sprintf;
 
 final class AggregateUnknown extends RepositoryException
 {
     /** @param class-string<AggregateRoot> $aggregateClass */
-    public function __construct(string $aggregateClass, string $aggregateId)
+    public function __construct(string $aggregateClass, AggregateRootId $aggregateId)
     {
         parent::__construct(
             sprintf(
                 'The aggregate %s with the ID "%s" was not loaded from this repository. Please reload the aggregate.',
                 $aggregateClass,
-                $aggregateId,
+                $aggregateId->toString(),
             ),
         );
     }

src/Repository/DefaultRepository.php

@@ -5,6 +5,7 @@
 namespace Patchlevel\EventSourcing\Repository;
 
 use Patchlevel\EventSourcing\Aggregate\AggregateRoot;
+use Patchlevel\EventSourcing\Aggregate\AggregateRootId;
 use Patchlevel\EventSourcing\Clock\SystemClock;
 use Patchlevel\EventSourcing\EventBus\Decorator\MessageDecorator;
 use Patchlevel\EventSourcing\EventBus\EventBus;
@@ -57,7 +58,7 @@ public function __construct(
     }
 
     /** @return T */
-    public function load(string $id): AggregateRoot
+    public function load(AggregateRootId $id): AggregateRoot
     {
         if ($this->snapshotStore && $this->metadata->snapshot) {
             try {
@@ -69,23 +70,23 @@ public function load(string $id): AggregateRoot
                     sprintf(
                         'snapshot for aggregate "%s" with the id "%s" not found',
                         $this->metadata->className,
-                        $id,
+                        $id->toString(),
                     ),
                 );
             } catch (SnapshotVersionInvalid) {
                 $this->logger->debug(
                     sprintf(
                         'snapshot for aggregate "%s" with the id "%s" is invalid',
                         $this->metadata->className,
-                        $id,
+                        $id->toString(),
                     ),
                 );
             }
         }
 
         $criteria = (new CriteriaBuilder())
             ->aggregateClass($this->metadata->className)
-            ->aggregateId($id)
+            ->aggregateId($id->toString())
             ->archived(false)
             ->build();
 
@@ -117,11 +118,11 @@ public function load(string $id): AggregateRoot
         return $aggregate;
     }
 
-    public function has(string $id): bool
+    public function has(AggregateRootId $id): bool
     {
         $criteria = (new CriteriaBuilder())
             ->aggregateClass($this->metadata->className)
-            ->aggregateId($id)
+            ->aggregateId($id->toString())
             ->build();
 
         return $this->store->count($criteria) > 0;
@@ -162,7 +163,7 @@ public function save(AggregateRoot $aggregate): void
                 static function (object $event) use ($aggregate, &$playhead, $messageDecorator, $clock) {
                     $message = Message::create($event)
                         ->withAggregateClass($aggregate::class)
-                        ->withAggregateId($aggregate->aggregateRootId())
+                        ->withAggregateId($aggregate->aggregateRootId()->toString())
                         ->withPlayhead(++$playhead)
                         ->withRecordedOn($clock->now());
 
@@ -194,15 +195,15 @@ static function (object $event) use ($aggregate, &$playhead, $messageDecorator,
      *
      * @return T
      */
-    private function loadFromSnapshot(string $aggregateClass, string $id): AggregateRoot
+    private function loadFromSnapshot(string $aggregateClass, AggregateRootId $id): AggregateRoot
     {
         assert($this->snapshotStore instanceof SnapshotStore);
 
         $aggregate = $this->snapshotStore->load($aggregateClass, $id);
 
         $criteria = (new CriteriaBuilder())
             ->aggregateClass($this->metadata->className)
-            ->aggregateId($id)
+            ->aggregateId($id->toString())
             ->fromPlayhead($aggregate->playhead())
             ->build();
 

src/Repository/PlayheadMismatch.php

@@ -4,18 +4,20 @@
 
 namespace Patchlevel\EventSourcing\Repository;
 
+use Patchlevel\EventSourcing\Aggregate\AggregateRootId;
+
 use function sprintf;
 
 final class PlayheadMismatch extends RepositoryException
 {
-    public function __construct(string $aggregateClass, string $aggregateId, int $playhead, int $eventCount)
+    public function __construct(string $aggregateClass, AggregateRootId $aggregateId, int $playhead, int $eventCount)
     {
         parent::__construct(sprintf(
             'There is a mismatch between the playhead [%s] and the event count [%s] for the aggregate [%s] with the id [%s]',
             $playhead,
             $eventCount,
             $aggregateClass,
-            $aggregateId,
+            $aggregateId->toString(),
         ));
     }
 }

src/Repository/Repository.php

@@ -5,14 +5,15 @@
 namespace Patchlevel\EventSourcing\Repository;
 
 use Patchlevel\EventSourcing\Aggregate\AggregateRoot;
+use Patchlevel\EventSourcing\Aggregate\AggregateRootId;
 
 /** @template T of AggregateRoot */
 interface Repository
 {
     /** @return T */
-    public function load(string $id): AggregateRoot;
+    public function load(AggregateRootId $id): AggregateRoot;
 
-    public function has(string $id): bool;
+    public function has(AggregateRootId $id): bool;
 
     /** @param T $aggregate */
     public function save(AggregateRoot $aggregate): void;