07. Introduction of QueryBus

.psalm-stubs/symfony-messenger.phpstub

@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Symfony\Component\Messenger\Stamp
+{
+    /** @template T */
+    final class HandledStamp implements StampInterface
+    {
+        /** @psam-return T */
+        public function getResult() { }
+    }
+}
+
+namespace Symfony\Component\Messenger
+{
+    trait HandleTrait
+    {
+        /**
+         * @template T
+         * @psalm-param object|Envelope $message
+         * @psalm-return T|Envelope<HandledStamp>
+         */
+        private function handle($message) { }
+    }
+}

config/packages/messenger.yaml

@@ -12,6 +12,9 @@ framework:
                     - doctrine_ping_connection
                     - doctrine_close_connection
                     - doctrine_transaction
+            query_bus:
+                middleware:
+                    - validation
 
         transports:
             # https://symfony.com/doc/current/messenger.html#transport-configuration

config/services.yaml

@@ -14,6 +14,8 @@ services:
             Cheeper\DomainModel\Follow\FollowRepository: '@Cheeper\Infrastructure\Persistence\DoctrineOrmFollowRepository'
             Cheeper\Application\EventBus: '@Cheeper\Infrastructure\Application\SymfonyMessengerEventBus'
             Redis: '@snc_redis.default'
+            Symfony\Component\Messenger\MessageBusInterface $commandBus: '@command_bus'
+            Symfony\Component\Messenger\MessageBusInterface $queryBus: '@query_bus'
 
     # makes classes in src/ available to be used as services
     # this creates a service per class whose id is the fully-qualified class name

psalm.xml

@@ -17,6 +17,7 @@
 
     <stubs>
         <file name=".psalm-stubs/phpredis.phpstub"/>
+        <file name=".psalm-stubs/symfony-messenger.phpstub"/>
     </stubs>
 
     <plugins>

src/App/Controller/GetFollowersCountController.php

@@ -6,6 +6,8 @@ namespace App\Controller;
 
 use Cheeper\Application\CountFollowers\CountFollowersQuery;
 use Cheeper\Application\CountFollowers\CountFollowersQueryHandler;
+use Cheeper\Application\CountFollowers\CountFollowersQueryResponse;
+use Cheeper\Application\QueryBus;
 use Cheeper\DomainModel\Author\AuthorDoesNotExist;
 use OpenApi\Attributes as OA;
 use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
@@ -19,6 +21,7 @@ final class GetFollowersCountController extends AbstractController
 
     public function __construct(
         private readonly CountFollowersQueryHandler $countFollowersQueryHandler,
+        private readonly QueryBus $queryBus,
     ) {
     }
 
@@ -50,15 +53,16 @@ final class GetFollowersCountController extends AbstractController
         $this->assertValidUuid($authorId);
 
         try {
-            $count = ($this->countFollowersQueryHandler)(
+            $response = $this->queryBus->askFor(
                 new CountFollowersQuery($authorId)
             );
+            assert($response instanceof CountFollowersQueryResponse);
         } catch (AuthorDoesNotExist $e) {
             throw $this->createNotFoundException($e->getMessage());
         }
 
         return $this->json([
-            'count' => $count,
+            'count' => $response->totalNumberOfFollowers,
         ]);
     }
 }

src/Cheeper/Application/CountFollowers/CountFollowersQueryHandler.php

@@ -4,6 +4,9 @@ declare(strict_types=1);
 
 namespace Cheeper\Application\CountFollowers;
 
+use Symfony\Component\Messenger\Attribute\AsMessageHandler;
+
+#[AsMessageHandler]
 final class CountFollowersQueryHandler
 {
     public function __construct(
@@ -11,10 +14,12 @@ final class CountFollowersQueryHandler
     ) {
     }
 
-    public function __invoke(CountFollowersQuery $query): int
+    public function __invoke(CountFollowersQuery $query): CountFollowersQueryResponse
     {
         $totalFollowers = $this->redis->get("followers_of:" . $query->authorId);
 
-        return false === $totalFollowers ? 0 : (int)$totalFollowers;
+        return new CountFollowersQueryResponse(
+            false === $totalFollowers ? 0 : (int)$totalFollowers
+        );
     }
 }

src/Cheeper/Application/CountFollowers/CountFollowersQueryResponse.php

@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Application\CountFollowers;
+
+use Cheeper\Application\QueryResponse;
+
+/** @psalm-immutable */
+final class CountFollowersQueryResponse implements QueryResponse
+{
+    public function __construct(
+        public readonly int $totalNumberOfFollowers
+    ) {
+    }
+}

src/Cheeper/Application/QueryBus.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Application;
+
+/**
+ * @template TQuery of Query
+ * @template TQueryResponse of QueryResponse
+ */
+interface QueryBus
+{
+    /**
+     * @psalm-param TQuery $query
+     * @psalm-return TQueryResponse
+     */
+    public function askFor(Query $query): QueryResponse;
+}

src/Cheeper/Application/QueryResponse.php

@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Application;
+
+/** @psalm-immutable */
+interface QueryResponse
+{
+}

src/Cheeper/Infrastructure/Application/SymfonyMessengerQueryBus.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Infrastructure\Application;
+
+use Cheeper\Application\Query;
+use Cheeper\Application\QueryBus;
+use Cheeper\Application\QueryResponse;
+use Symfony\Component\Messenger\Envelope;
+use Symfony\Component\Messenger\Exception\LogicException;
+use Symfony\Component\Messenger\HandleTrait;
+use Symfony\Component\Messenger\MessageBusInterface;
+use Symfony\Component\Messenger\Stamp\HandledStamp;
+
+final class SymfonyMessengerQueryBus implements QueryBus
+{
+    use HandleTrait;
+
+    public function __construct(
+        MessageBusInterface $queryBus
+    ) {
+        $this->messageBus = $queryBus;
+    }
+
+    public function askFor(Query $query): QueryResponse
+    {
+        $result = $this->handle($query);
+        assert($result instanceof QueryResponse);
+
+        return $result;
+    }
+}

tests/Cheeper/Tests/Application/CountFollowersQueryHandlerTest.php

@@ -98,10 +98,10 @@ final class CountFollowersQueryHandlerTest extends TestCase
 
         Iter\apply($events, ($this->authorWasFollowedEventHandler)(...));
 
-        $totalNumberOfFollowers = ($this->countFollowersQueryHandler)(
+        $queryResponse = ($this->countFollowersQueryHandler)(
             new CountFollowersQuery($authorId)
         );
 
-        $this->assertSame(3, $totalNumberOfFollowers);
+        $this->assertSame(3, $queryResponse->totalNumberOfFollowers);
     }
 }