diff --git a/README.md b/README.md
index 0499290..04c6e35 100644
--- a/README.md
+++ b/README.md
@@ -40,3 +40,24 @@ And to stop all services just run
 
 This code can also be run using Symfony Local Webserver.
 
+### Fixtures 
+
+    make database
+
+#### Adding Authors
+
+    http --json --verify false POST https://127.0.0.1:8000/chapter7/author author_id="a64a52cc-3ee9-4a15-918b-099e18b43119" username="bob" email="bob@bob.com"
+    http --json --verify false POST https://127.0.0.1:8000/chapter7/author author_id="1fd7d739-2ad7-41a8-8c18-565603e3733f" username="alice" email="alice@alice.com"
+    http --json --verify false POST https://127.0.0.1:8000/chapter7/author author_id="1da1366f-b066-4514-9b29-7346df41e371" username="charlie" email="charlie@charlie.com"
+
+#### Posting Cheeps
+
+    http --json --verify false POST https://127.0.0.1:8000/chapter7/cheep cheep_id="28bc90bd-2dfb-4b71-962f-81f02b0b3149" author_id="a64a52cc-3ee9-4a15-918b-099e18b43119" message="Hello world! This is Bob!"
+    http --json --verify false POST https://127.0.0.1:8000/chapter7/cheep cheep_id="04efc3af-59a3-4695-803f-d37166c3af56" author_id="1fd7d739-2ad7-41a8-8c18-565603e3733f" message="Hello world! This is Alice!"
+    http --json --verify false POST https://127.0.0.1:8000/chapter7/cheep cheep_id="8a5539e6-3be2-4fa7-906e-179efcfca46b" author_id="1da1366f-b066-4514-9b29-7346df41e371" message="Hello world! This is Charlie!"
+
+#### Following other Authors
+
+    http --json --verify false POST https://127.0.0.1:8000/chapter7/follow follow_id="8cc71bf2-f827-4c92-95a5-43bb1bc622ad" from_author_id="a64a52cc-3ee9-4a15-918b-099e18b43119" to_author_id="1fd7d739-2ad7-41a8-8c18-565603e3733f"
+    http --json --verify false POST https://127.0.0.1:8000/chapter7/follow follow_id="f3088920-841e-4577-a3c2-efdc80f0dea5" from_author_id="a64a52cc-3ee9-4a15-918b-099e18b43119" to_author_id="1da1366f-b066-4514-9b29-7346df41e371"
+    http --json --verify false POST https://127.0.0.1:8000/chapter7/follow follow_id="45ea9e38-d821-4c8c-8619-362bf57f4c56" from_author_id="1fd7d739-2ad7-41a8-8c18-565603e3733f" to_author_id="a64a52cc-3ee9-4a15-918b-099e18b43119"
diff --git a/config/packages/doctrine.yaml b/config/packages/doctrine.yaml
index 7f18c59..1d5cd1a 100644
--- a/config/packages/doctrine.yaml
+++ b/config/packages/doctrine.yaml
@@ -23,3 +23,9 @@ doctrine:
                 dir: '%kernel.project_dir%/src/Cheeper/Infrastructure/Persistence/doctrine-mappings'
                 prefix: 'Cheeper\DomainModel'
                 alias: CheeperDomainModel
+            CheeperChapter7DomainModel:
+                is_bundle: false
+                type: xml
+                dir: '%kernel.project_dir%/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineMappings'
+                prefix: 'Cheeper\Chapter7\DomainModel'
+                alias: CheeperChapter7DomainModel
diff --git a/config/packages/messenger.yaml b/config/packages/messenger.yaml
index ed4b427..4129df9 100644
--- a/config/packages/messenger.yaml
+++ b/config/packages/messenger.yaml
@@ -37,9 +37,10 @@ framework:
             Cheeper\Application\Command\AsyncCommand: async_commands
             Cheeper\Application\Command\SyncCommand: sync_commands
 
-            # Cheeper\Chapter7\Application\Command\Author\SignUp: chapter7_sync_commands
-            Cheeper\Chapter7\Application\Command\Author\SignUp: chapter7_async_commands
-            Cheeper\Chapter7\Application\Command\Author\Follow: chapter7_async_commands
+            # Cheeper\Chapter7\Application\Command\Author\SignUp: chapter7_async_commands
+            Cheeper\Chapter7\Application\Command\Author\SignUp: chapter7_sync_commands
+            Cheeper\Chapter7\Application\Command\Author\Follow: chapter7_sync_commands
+            Cheeper\Chapter7\Application\Command\Cheep\PostCheep: chapter7_sync_commands
 
             # Domain Events are sent to asynchronous
             # transport to be processed later.
diff --git a/config/services.yaml b/config/services.yaml
index 69a560e..584b58c 100644
--- a/config/services.yaml
+++ b/config/services.yaml
@@ -17,6 +17,9 @@ services:
             # ignore
             Cheeper\DomainModel\Cheep\Cheeps $cheeps: '@Cheeper\Infrastructure\Persistence\DoctrineOrmCheeps'
             Cheeper\DomainModel\Author\Authors $authors: '@Cheeper\Infrastructure\Persistence\DoctrineOrmAuthors'
+            Cheeper\Chapter7\DomainModel\Author\Authors $authors: '@Cheeper\Chapter7\Infrastructure\Persistence\DoctrineOrmAuthors'
+            Cheeper\Chapter7\DomainModel\Cheep\Cheeps $cheeps: '@Cheeper\Chapter7\Infrastructure\Persistence\DoctrineOrmCheeps'
+            Cheeper\Chapter7\DomainModel\Follow\Follows $follows: '@Cheeper\Chapter7\Infrastructure\Persistence\DoctrineOrmFollows'
             Cheeper\DomainModel\Author\Authors $authorsRepository: '@Cheeper\Infrastructure\Persistence\DoctrineOrmAuthors'
             Cheeper\DomainModel\Follow\Follows $follows: '@Cheeper\Infrastructure\Persistence\DoctrineOrmFollows'
             #end-ignore
@@ -99,11 +102,25 @@ services:
             - { name: messenger.message_handler, bus: event.bus }
         class: 'Cheeper\Chapter6\Infrastructure\Application\Projector\Author\SymfonyAuthorFollowedHandler'
 
+    # CHAPTER 7
+    Cheeper\Chapter7\Infrastructure\:
+        resource: '../src/Cheeper/Chapter7/Infrastructure/**/*.php'
+
     Cheeper\Chapter7\Application\Command\Author\SignUpHandler:
         tags:
             - { name: messenger.message_handler, bus: command.bus }
         class: 'Cheeper\Chapter7\Application\Command\Author\SignUpHandler'
 
+    Cheeper\Chapter7\Application\Command\Cheep\PostCheepHandler:
+        tags:
+            - { name: messenger.message_handler, bus: command.bus }
+        class: 'Cheeper\Chapter7\Application\Command\Cheep\PostCheepHandler'
+
+    Cheeper\Chapter7\Application\Command\Author\FollowHandler:
+        tags:
+            - { name: messenger.message_handler, bus: command.bus }
+        class: 'Cheeper\Chapter7\Application\Command\Author\FollowHandler'
+
     App\EventListener\UserCreatedListener:
         tags:
             - name: "doctrine.orm.entity_listener"
diff --git a/src/App/Controller/Chapter7/DefaultController.php b/src/App/Controller/Chapter7/DefaultController.php
deleted file mode 100644
index 42af9c7..0000000
--- a/src/App/Controller/Chapter7/DefaultController.php
+++ /dev/null
@@ -1,37 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace App\Controller\Chapter7;
-
-use App\Messenger\CommandBus;
-use Cheeper\Chapter7\DomainModel\Follow\Follow;
-use Cheeper\DomainModel\Author\AuthorId;
-use Cheeper\DomainModel\Follow\FollowId;
-use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
-use Symfony\Component\HttpFoundation\Request;
-use Symfony\Component\HttpFoundation\Response;
-use Symfony\Component\Routing\Annotation\Route;
-
-final class DefaultController extends AbstractController
-{
-    public function __construct(
-        private CommandBus $commandBus
-    )
-    {
-    }
-
-    #[Route("/chapter7/follow", methods: ["POST"])]
-    public function follow(Request $request): Response
-    {
-        $this->commandBus->handle(
-            Follow::fromAuthorToAuthor(
-                FollowId::nextIdentity(),
-                AuthorId::nextIdentity(),
-                AuthorId::nextIdentity(),
-            )
-        );
-
-        return $this->json("hello");
-    }
-}
diff --git a/src/App/Controller/Chapter7/FollowAuthorController.php b/src/App/Controller/Chapter7/FollowAuthorController.php
new file mode 100644
index 0000000..b1441c9
--- /dev/null
+++ b/src/App/Controller/Chapter7/FollowAuthorController.php
@@ -0,0 +1,60 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Controller\Chapter7;
+
+use App\Messenger\CommandBus;
+use Cheeper\Chapter7\Application\Command\Author\Follow;
+use Cheeper\Chapter7\Application\Command\Cheep\PostCheep;
+use Cheeper\DomainModel\Author\AuthorDoesNotExist;
+use InvalidArgumentException;
+use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+use Symfony\Component\HttpFoundation\JsonResponse;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\Routing\Annotation\Route;
+
+final class FollowAuthorController extends AbstractController
+{
+    #[Route("/chapter7/follow", methods: ["POST"])]
+    public function __invoke(Request $request, CommandBus $commandBus): Response
+    {
+        $httpCode = Response::HTTP_ACCEPTED;
+        try {
+            $command = Follow::fromArray(
+                $this->getRequestContentInJson($request)
+            );
+
+            $commandBus->handle($command);
+
+            $httpContent = [
+                'message_id' => $command->messageId()?->toString()
+            ];
+        } catch (
+            AuthorDoesNotExist
+            |InvalidArgumentException $exception
+        ) {
+            $httpCode = Response::HTTP_INTERNAL_SERVER_ERROR;
+            $httpContent = ['message' => $exception->getMessage()];
+        }
+
+        return $this->buildJsonResponse($httpContent, $httpCode);
+    }
+
+    private function getRequestContentInJson(Request $request): mixed
+    {
+        return \Safe\json_decode(
+            $request->getContent(),
+            true
+        );
+    }
+
+    private function buildJsonResponse(array $httpContent, int $httpCode): JsonResponse
+    {
+        return $this->json(
+            data: $httpContent,
+            status: $httpCode,
+        );
+    }
+}
diff --git a/src/App/Controller/Chapter7/PostCheepController.php b/src/App/Controller/Chapter7/PostCheepController.php
new file mode 100644
index 0000000..227e64f
--- /dev/null
+++ b/src/App/Controller/Chapter7/PostCheepController.php
@@ -0,0 +1,59 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Controller\Chapter7;
+
+use App\Messenger\CommandBus;
+use Cheeper\Chapter7\Application\Command\Cheep\PostCheep;
+use Cheeper\DomainModel\Author\AuthorDoesNotExist;
+use InvalidArgumentException;
+use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+use Symfony\Component\HttpFoundation\JsonResponse;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\Routing\Annotation\Route;
+
+final class PostCheepController extends AbstractController
+{
+    #[Route("/chapter7/cheep", methods: ["POST"])]
+    public function __invoke(Request $request, CommandBus $commandBus): Response
+    {
+        $httpCode = Response::HTTP_ACCEPTED;
+        try {
+            $command = PostCheep::fromArray(
+                $this->getRequestContentInJson($request)
+            );
+
+            $commandBus->handle($command);
+            $httpContent = [
+                'message_id' => $command->messageId()?->toString(),
+                'cheep_id' => $command->authorId(),
+            ];
+        } catch (
+            AuthorDoesNotExist
+            |InvalidArgumentException $exception
+        ) {
+            $httpCode = Response::HTTP_INTERNAL_SERVER_ERROR;
+            $httpContent = ['message' => $exception->getMessage()];
+        }
+
+        return $this->buildJsonResponse($httpContent, $httpCode);
+    }
+
+    private function getRequestContentInJson(Request $request): mixed
+    {
+        return \Safe\json_decode(
+            $request->getContent(),
+            true
+        );
+    }
+
+    private function buildJsonResponse(array $httpContent, int $httpCode): JsonResponse
+    {
+        return $this->json(
+            data: $httpContent,
+            status: $httpCode,
+        );
+    }
+}
diff --git a/src/App/Controller/Chapter7/SignUpAuthorController.php b/src/App/Controller/Chapter7/SignUpAuthorController.php
index d2067ca..6f4a4e4 100644
--- a/src/App/Controller/Chapter7/SignUpAuthorController.php
+++ b/src/App/Controller/Chapter7/SignUpAuthorController.php
@@ -6,7 +6,10 @@ namespace App\Controller\Chapter7;
 
 use App\Messenger\CommandBus;
 use Cheeper\Chapter7\Application\Command\Author\SignUp;
+use Cheeper\DomainModel\Author\AuthorAlreadyExists;
+use InvalidArgumentException;
 use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+use Symfony\Component\HttpFoundation\JsonResponse;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\Routing\Annotation\Route;
@@ -14,21 +17,28 @@ use Symfony\Component\Routing\Annotation\Route;
 final class SignUpAuthorController extends AbstractController
 {
     #[Route("/chapter7/author", methods: ["POST"])]
-    public function follow(Request $request, CommandBus $commandBus): Response
+    public function __invoke(Request $request, CommandBus $commandBus): Response
     {
-        $command = SignUp::fromArray(
-            $this->getRequestContentInJson($request)
-        );
+        $httpCode = Response::HTTP_ACCEPTED;
+        try {
+            $command = SignUp::fromArray(
+                $this->getRequestContentInJson($request)
+            );
 
-        $commandBus->handle($command);
-
-        return $this->json(
-            data: [
-                'message_id' => $command->messageId()->toString(),
+            $commandBus->handle($command);
+            $httpContent = [
+                'message_id' => $command->messageId()?->toString(),
                 'author_id' => $command->authorId(),
-            ],
-            status: Response::HTTP_CREATED,
-        );
+            ];
+        } catch (
+            AuthorAlreadyExists
+            |InvalidArgumentException $exception
+        ) {
+            $httpCode = Response::HTTP_INTERNAL_SERVER_ERROR;
+            $httpContent = ['message' => $exception->getMessage()];
+        }
+
+        return $this->buildJsonResponse($httpContent, $httpCode);
     }
 
     private function getRequestContentInJson(Request $request): mixed
@@ -38,5 +48,13 @@ final class SignUpAuthorController extends AbstractController
             true
         );
     }
+
+    private function buildJsonResponse(array $httpContent, int $httpCode): JsonResponse
+    {
+        return $this->json(
+            data: $httpContent,
+            status: $httpCode,
+        );
+    }
 }
 
diff --git a/src/App/Messenger/FromScratch.php b/src/App/Messenger/FromScratch.php
index 1927599..e254e8a 100644
--- a/src/App/Messenger/FromScratch.php
+++ b/src/App/Messenger/FromScratch.php
@@ -2,6 +2,8 @@
 
 declare(strict_types=1);
 
+namespace App\Messenger;
+
 use Cheeper\Application\Command\Cheep\PostCheep;
 use Cheeper\Application\Command\Cheep\PostCheepHandler;
 use Cheeper\Chapter6\Infrastructure\Application\Event\InMemoryEventBus;
diff --git a/src/Cheeper/Chapter7/Application/Command/Author/Follow.php b/src/Cheeper/Chapter7/Application/Command/Author/Follow.php
index 8ce7797..4be235a 100644
--- a/src/Cheeper/Chapter7/Application/Command/Author/Follow.php
+++ b/src/Cheeper/Chapter7/Application/Command/Author/Follow.php
@@ -5,15 +5,18 @@ declare(strict_types=1);
 namespace Cheeper\Chapter7\Application\Command\Author;
 
 use Cheeper\Chapter7\Application\MessageTrait;
+use Cheeper\DomainModel\Follow\FollowId;
 
 final class Follow
 {
     use MessageTrait;
 
     private function __construct(
+        private string $followId,
         private string $fromAuthorId,
         private string $toAuthorId
     ) {
+        $this->stampAsNewMessage();
     }
 
     public function fromAuthorId(): string
@@ -26,8 +29,22 @@ final class Follow
         return $this->toAuthorId;
     }
 
+    public function followId(): string
+    {
+        return $this->followId;
+    }
+
     public static function fromAuthorIdToAuthorId(string $from, string $to): self
     {
-        return new self($from, $to);
+        return new self($from, $to, FollowId::nextIdentity()->toString());
     }
-}
+
+    public static function fromArray(array $array): self
+    {
+        return new self(
+            $array['follow_id'] ?? '',
+            $array['from_author_id'] ?? '',
+            $array['to_author_id'] ?? '',
+        );
+    }
+}
\ No newline at end of file
diff --git a/src/Cheeper/Chapter7/Application/Command/Author/FollowHandler.php b/src/Cheeper/Chapter7/Application/Command/Author/FollowHandler.php
index 0663826..f3d3f6f 100644
--- a/src/Cheeper/Chapter7/Application/Command/Author/FollowHandler.php
+++ b/src/Cheeper/Chapter7/Application/Command/Author/FollowHandler.php
@@ -5,11 +5,11 @@ declare(strict_types=1);
 namespace Cheeper\Chapter7\Application\Command\Author;
 
 use Cheeper\Chapter6\Application\Event\EventBus;
-use Cheeper\DomainModel\Author\Author;
+use Cheeper\Chapter7\DomainModel\Author\Author;
+use Cheeper\Chapter7\DomainModel\Author\Authors;
+use Cheeper\Chapter7\DomainModel\Follow\Follows;
 use Cheeper\DomainModel\Author\AuthorDoesNotExist;
 use Cheeper\DomainModel\Author\AuthorId;
-use Cheeper\DomainModel\Author\Authors;
-use Cheeper\DomainModel\Follow\Follows;
 
 final class FollowHandler
 {
diff --git a/src/Cheeper/Chapter7/Application/Command/Author/SignUp.php b/src/Cheeper/Chapter7/Application/Command/Author/SignUp.php
index c5c8cc4..f920e01 100644
--- a/src/Cheeper/Chapter7/Application/Command/Author/SignUp.php
+++ b/src/Cheeper/Chapter7/Application/Command/Author/SignUp.php
@@ -23,6 +23,7 @@ final class SignUp
         private ?string $website = null,
         private ?string $birthDate = null,
     ) {
+        $this->stampAsNewMessage();
     }
 
     //ignore
@@ -68,11 +69,11 @@ final class SignUp
 
     public static function fromArray(array $array): self
     {
-        return (new self(
+        return new self(
             $array['author_id'] ?? '',
             $array['username'] ?? '',
             $array['email'] ?? '',
-        ))->stampAsNewMessage();
+        );
     }
     //end-ignore
 }
diff --git a/src/Cheeper/Chapter7/Application/Command/Author/SignUpHandler.php b/src/Cheeper/Chapter7/Application/Command/Author/SignUpHandler.php
index b37ec5b..b236b66 100644
--- a/src/Cheeper/Chapter7/Application/Command/Author/SignUpHandler.php
+++ b/src/Cheeper/Chapter7/Application/Command/Author/SignUpHandler.php
@@ -5,10 +5,10 @@ declare(strict_types=1);
 namespace Cheeper\Chapter7\Application\Command\Author;
 
 use Cheeper\Chapter6\Application\Event\EventBus;
-use Cheeper\DomainModel\Author\Author;
+use Cheeper\Chapter7\DomainModel\Author\Author;
+use Cheeper\Chapter7\DomainModel\Author\Authors;
 use Cheeper\DomainModel\Author\AuthorAlreadyExists;
 use Cheeper\DomainModel\Author\AuthorId;
-use Cheeper\DomainModel\Author\Authors;
 use Cheeper\DomainModel\Author\BirthDate;
 use Cheeper\DomainModel\Author\EmailAddress;
 use Cheeper\DomainModel\Author\UserName;
diff --git a/src/Cheeper/Chapter7/Application/Command/Cheep/PostCheep.php b/src/Cheeper/Chapter7/Application/Command/Cheep/PostCheep.php
new file mode 100644
index 0000000..11b5ec9
--- /dev/null
+++ b/src/Cheeper/Chapter7/Application/Command/Cheep/PostCheep.php
@@ -0,0 +1,46 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Application\Command\Cheep;
+
+use Cheeper\Chapter7\Application\MessageTrait;
+
+//snippet post-cheep
+final class PostCheep
+{
+    use MessageTrait;
+
+    private function __construct(
+        private string $cheepId,
+        private string $authorId,
+        private string $message,
+    ) {
+        $this->stampAsNewMessage();
+    }
+
+    public static function fromArray(array $array): self
+    {
+        return new self(
+            $array['cheep_id'] ?? '',
+            $array['author_id'] ?? '',
+            $array['message'] ?? '',
+        );
+    }
+
+    public function cheepId(): string
+    {
+        return $this->cheepId;
+    }
+
+    public function authorId(): string
+    {
+        return $this->authorId;
+    }
+
+    public function message(): string
+    {
+        return $this->message;
+    }
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter7/Application/Command/Cheep/PostCheepHandler.php b/src/Cheeper/Chapter7/Application/Command/Cheep/PostCheepHandler.php
new file mode 100644
index 0000000..b78ac7a
--- /dev/null
+++ b/src/Cheeper/Chapter7/Application/Command/Cheep/PostCheepHandler.php
@@ -0,0 +1,49 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Application\Command\Cheep;
+
+use Cheeper\Chapter6\Application\Event\EventBus;
+use Cheeper\Chapter7\DomainModel\Author\Author;
+use Cheeper\Chapter7\DomainModel\Author\Authors;
+use Cheeper\Chapter7\DomainModel\Cheep\Cheep;
+use Cheeper\Chapter7\DomainModel\Cheep\Cheeps;
+use Cheeper\DomainModel\Author\AuthorDoesNotExist;
+use Cheeper\DomainModel\Author\AuthorId;
+use Cheeper\DomainModel\Cheep\CheepId;
+use Cheeper\DomainModel\Cheep\CheepMessage;
+
+//snippet post-cheep-handler
+final class PostCheepHandler
+{
+    public function __construct(
+        private Authors $authors,
+        private Cheeps $cheeps,
+        private EventBus $eventBus
+    ) {
+    }
+
+    public function __invoke(PostCheep $command): void
+    {
+        $authorId = AuthorId::fromString($command->authorId());
+        $cheepId = CheepId::fromString($command->cheepId());
+        $message = CheepMessage::write($command->message());
+
+        $author = $this->authors->ofId($authorId);
+        $this->checkAuthorExists($author, $authorId);
+
+        $cheep = Cheep::compose($authorId, $cheepId, $message);
+        $this->cheeps->add($cheep);
+
+        $this->eventBus->notifyAll($cheep->domainEvents());
+    }
+
+    private function checkAuthorExists(?Author $author, AuthorId $authorId): void
+    {
+        if (null === $author) {
+            throw AuthorDoesNotExist::withAuthorIdOf($authorId);
+        }
+    }
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter7/DomainModel/Author/Author.php b/src/Cheeper/Chapter7/DomainModel/Author/Author.php
index abfb442..9c0b092 100644
--- a/src/Cheeper/Chapter7/DomainModel/Author/Author.php
+++ b/src/Cheeper/Chapter7/DomainModel/Author/Author.php
@@ -5,32 +5,126 @@ declare(strict_types=1);
 namespace Cheeper\Chapter7\DomainModel\Author;
 
 use Cheeper\Chapter7\DomainModel\Follow\Follow;
-use Cheeper\DomainModel\Author\Author as AuthorChapter6;
 use Cheeper\DomainModel\Author\AuthorId;
+use Cheeper\DomainModel\Author\BirthDate;
+use Cheeper\DomainModel\Author\EmailAddress;
+use Cheeper\DomainModel\Author\UserName;
+use Cheeper\DomainModel\Author\Website;
 use Cheeper\DomainModel\Follow\FollowId;
+use Cheeper\DomainModel\TriggerEventsTrait;
 use DateTimeImmutable;
+use InvalidArgumentException;
 
-class Author extends AuthorChapter6
+final class Author
 {
-    protected function __construct(
-        protected string             $authorId,
-        protected string             $userName,
-        protected string             $email,
-        protected ?string            $name = null,
-        protected ?string            $biography = null,
-        protected ?string            $location = null,
-        protected ?string            $website = null,
-        protected ?DateTimeImmutable $birthDate = null,
+    use TriggerEventsTrait;
+
+    private function __construct(
+        private string             $authorId,
+        private string             $userName,
+        private string             $email,
+        private ?string            $name = null,
+        private ?string            $biography = null,
+        private ?string            $location = null,
+        private ?string            $website = null,
+        private ?DateTimeImmutable $birthDate = null,
     ) {
         $this->setName($name);
         $this->setBiography($biography);
         $this->setLocation($location);
 
         $this->notifyDomainEvent(
-            NewAuthorSigned::fromAuthor($this)
+            $this->buildNewAuthorSignedDomainEvent()
         );
     }
 
+    protected function buildNewAuthorSignedDomainEvent(): NewAuthorSigned
+    {
+        return NewAuthorSigned::fromAuthor($this);
+    }
+
+    public static function signUp(
+        AuthorId $authorId,
+        UserName $userName,
+        EmailAddress $email,
+        ?string $name = null,
+        ?string $biography = null,
+        ?string $location = null,
+        ?Website $website = null,
+        ?BirthDate $birthDate = null
+    ): static {
+        return new static(
+            $authorId->toString(),
+            $userName->userName(),
+            $email->value(),
+            $name,
+            $biography,
+            $location,
+            $website?->toString(),
+            $birthDate?->date()
+        );
+    }
+
+    protected function setName(?string $name): void
+    {
+        $this->name = $this->checkIsNotNull($name, 'Name cannot be empty');
+    }
+
+    protected function setBiography(?string $biography): void
+    {
+        $this->biography = $this->checkIsNotNull($biography, 'Biography cannot be empty');
+    }
+
+    protected function setLocation(?string $location): void
+    {
+        $this->location = $this->checkIsNotNull($location, 'Location cannot be empty');
+    }
+
+    public function authorId(): AuthorId
+    {
+        return AuthorId::fromString($this->authorId);
+    }
+
+    public function userId(): AuthorId
+    {
+        return AuthorId::fromString($this->authorId);
+    }
+
+    public function userName(): UserName
+    {
+        return UserName::pick($this->userName);
+    }
+
+    public function email(): EmailAddress
+    {
+        return EmailAddress::from($this->email);
+    }
+
+    public function name(): ?string
+    {
+        return $this->name;
+    }
+
+    public function biography(): ?string
+    {
+        return $this->biography;
+    }
+
+    public function location(): ?string
+    {
+        return $this->location;
+    }
+
+    public function website(): ?Website
+    {
+        return $this->website !== null ? Website::fromString($this->website) : null;
+    }
+
+    public function birthDate(): ?BirthDate
+    {
+        return $this->birthDate !== null ? BirthDate::fromString($this->birthDate->format('Y-m-d')) : null;
+    }
+
     public function followAuthorId(AuthorId $toFollow): Follow
     {
         return Follow::fromAuthorToAuthor(
@@ -39,4 +133,13 @@ class Author extends AuthorChapter6
             toAuthorId: $toFollow
         );
     }
-}
+
+    private function checkIsNotNull(?string $value, string $errorMessage): ?string
+    {
+        if ('' === $value) {
+            throw new InvalidArgumentException($errorMessage);
+        }
+
+        return $value;
+    }
+}
\ No newline at end of file
diff --git a/src/Cheeper/Chapter7/DomainModel/Author/Authors.php b/src/Cheeper/Chapter7/DomainModel/Author/Authors.php
new file mode 100644
index 0000000..2d8b219
--- /dev/null
+++ b/src/Cheeper/Chapter7/DomainModel/Author/Authors.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\DomainModel\Author;
+
+use Cheeper\DomainModel\Author\AuthorId;
+use Cheeper\DomainModel\Author\UserName;
+
+//snippet authors
+interface Authors
+{
+    public function ofId(AuthorId $authorId): ?Author;
+    public function ofUserName(UserName $userName): ?Author;
+    public function add(Author $author): void;
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter7/DomainModel/Author/NewAuthorSigned.php b/src/Cheeper/Chapter7/DomainModel/Author/NewAuthorSigned.php
index fc7d742..50e6222 100644
--- a/src/Cheeper/Chapter7/DomainModel/Author/NewAuthorSigned.php
+++ b/src/Cheeper/Chapter7/DomainModel/Author/NewAuthorSigned.php
@@ -5,9 +5,39 @@ declare(strict_types=1);
 namespace Cheeper\Chapter7\DomainModel\Author;
 
 use Cheeper\Chapter7\Application\MessageTrait;
-use Cheeper\DomainModel\Author\NewAuthorSigned as NewAuthorSignedChapter6;
+use Cheeper\DomainModel\DomainEvent;
+use DateTimeImmutable;
+use DateTimeZone;
 
-final class NewAuthorSigned extends NewAuthorSignedChapter6
+// snippet new-author-signed-domain-event
+class NewAuthorSigned implements DomainEvent
 {
     use MessageTrait;
+
+    private function __construct(
+        private string $authorId,
+        private DateTimeImmutable $occurredOn
+    ) {
+    }
+
+    public static function fromAuthor(Author $author): static
+    {
+        return new static(
+            $author->authorId()->toString(),
+            new DateTimeImmutable(
+                timezone: new DateTimeZone("UTC")
+            )
+        );
+    }
+
+    public function authorId(): string
+    {
+        return $this->authorId;
+    }
+
+    public function occurredOn(): DateTimeImmutable
+    {
+        return $this->occurredOn;
+    }
 }
+// end-snippet
diff --git a/src/Cheeper/Chapter7/DomainModel/Cheep/Cheep.php b/src/Cheeper/Chapter7/DomainModel/Cheep/Cheep.php
new file mode 100644
index 0000000..891a125
--- /dev/null
+++ b/src/Cheeper/Chapter7/DomainModel/Cheep/Cheep.php
@@ -0,0 +1,66 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\DomainModel\Cheep;
+
+use Cheeper\DomainModel\Author\AuthorId;
+use Cheeper\DomainModel\Cheep\CheepDate;
+use Cheeper\DomainModel\Cheep\CheepId;
+use Cheeper\DomainModel\Cheep\CheepMessage;
+use Cheeper\DomainModel\TriggerEventsTrait;
+
+class Cheep
+{
+    use TriggerEventsTrait;
+
+    private function __construct(
+        private AuthorId $authorId,
+        private CheepId $cheepId,
+        private CheepMessage $cheepMessage,
+        private CheepDate $cheepDate,
+    ) {
+        $this->notifyDomainEvent(
+            CheepPosted::fromCheep($this)
+        );
+    }
+
+    public static function compose(AuthorId $authorId, CheepId $cheepId, CheepMessage $cheepMessage): self
+    {
+        $cheepDate = new CheepDate(
+            (new \DateTimeImmutable(timezone: new \DateTimeZone('UTC')))->format('Y-m-d H:i:s')
+        );
+
+        return new self(
+            $authorId,
+            $cheepId,
+            $cheepMessage,
+            $cheepDate
+        );
+    }
+
+    final public function authorId(): AuthorId
+    {
+        return $this->authorId;
+    }
+
+    final public function cheepId(): CheepId
+    {
+        return $this->cheepId;
+    }
+
+    final public function cheepMessage(): CheepMessage
+    {
+        return $this->cheepMessage;
+    }
+
+    final public function cheepDate(): CheepDate
+    {
+        return $this->cheepDate;
+    }
+
+    final public function recomposeWith(CheepMessage $cheepMessage): void
+    {
+        $this->cheepMessage = $cheepMessage;
+    }
+}
diff --git a/src/Cheeper/Chapter7/DomainModel/Cheep/CheepPosted.php b/src/Cheeper/Chapter7/DomainModel/Cheep/CheepPosted.php
new file mode 100644
index 0000000..8e2cfd5
--- /dev/null
+++ b/src/Cheeper/Chapter7/DomainModel/Cheep/CheepPosted.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\DomainModel\Cheep;
+
+use Cheeper\Chapter7\Application\MessageTrait;
+use Cheeper\DomainModel\DomainEvent;
+use DateTimeImmutable;
+use DateTimeZone;
+
+// snippet cheep-posted-domain-event
+final class CheepPosted implements DomainEvent
+{
+    use MessageTrait;
+
+    private function __construct(
+        private string $cheepId,
+        private string $authorId,
+        private string $cheepMessage,
+        private string $cheepDate,
+        private DateTimeImmutable $occurredOn
+    ) {
+        $this->stampAsNewMessage();
+    }
+
+    public static function fromCheep(Cheep $cheep): self
+    {
+        return new self(
+            $cheep->cheepId()->toString(),
+            $cheep->authorId()->toString(),
+            $cheep->cheepMessage()->message(),
+            $cheep->cheepDate()->date(),
+            new DateTimeImmutable(
+                timezone: new DateTimeZone("UTC")
+            )
+        );
+    }
+
+    public function cheepId(): string
+    {
+        return $this->cheepId;
+    }
+
+    public function authorId(): string
+    {
+        return $this->authorId;
+    }
+
+    public function cheepMessage(): string
+    {
+        return $this->cheepMessage;
+    }
+
+    public function cheepDate(): string
+    {
+        return $this->cheepDate;
+    }
+
+    public function occurredOn(): DateTimeImmutable
+    {
+        return $this->occurredOn;
+    }
+}
+// end-snippet
diff --git a/src/Cheeper/Chapter7/DomainModel/Cheep/Cheeps.php b/src/Cheeper/Chapter7/DomainModel/Cheep/Cheeps.php
new file mode 100644
index 0000000..e664620
--- /dev/null
+++ b/src/Cheeper/Chapter7/DomainModel/Cheep/Cheeps.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\DomainModel\Cheep;
+
+use Cheeper\DomainModel\Cheep\CheepId;
+
+//snippet cheeps
+interface Cheeps
+{
+    public function add(Cheep $cheep): void;
+    public function ofId(CheepId $cheepId): ?Cheep;
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter7/DomainModel/Follow/AuthorFollowed.php b/src/Cheeper/Chapter7/DomainModel/Follow/AuthorFollowed.php
index 17f40dd..d4b6272 100644
--- a/src/Cheeper/Chapter7/DomainModel/Follow/AuthorFollowed.php
+++ b/src/Cheeper/Chapter7/DomainModel/Follow/AuthorFollowed.php
@@ -19,6 +19,7 @@ final class AuthorFollowed implements DomainEvent
         private string $toAuthorId,
         private DateTimeImmutable $occurredOn
     ) {
+        $this->stampAsNewMessage();
     }
 
     public static function fromFollow(Follow $follow): self
diff --git a/src/Cheeper/Chapter7/DomainModel/Follow/Follow.php b/src/Cheeper/Chapter7/DomainModel/Follow/Follow.php
index 1bdb617..e57e102 100644
--- a/src/Cheeper/Chapter7/DomainModel/Follow/Follow.php
+++ b/src/Cheeper/Chapter7/DomainModel/Follow/Follow.php
@@ -4,23 +4,68 @@ declare(strict_types=1);
 
 namespace Cheeper\Chapter7\DomainModel\Follow;
 
-use Cheeper\DomainModel\Follow\Follow as FollowChapter6;
 use Cheeper\DomainModel\Author\AuthorId;
 use Cheeper\DomainModel\Follow\FollowId;
 use Cheeper\DomainModel\TriggerEventsTrait;
 
-class Follow extends FollowChapter6
+// snippet follow-entity-with-events
+final class Follow
 {
     use TriggerEventsTrait;
 
     protected function __construct(
-        protected FollowId $followId,
-        protected AuthorId $fromAuthorId,
-        protected AuthorId $toAuthorId,
+        private string $followId,
+        private string $fromAuthorId,
+        private string $toAuthorId,
     ) {
         $this->notifyDomainEvent(
             AuthorFollowed::fromFollow($this)
-                ->stampAsNewMessage()
+        );
+
+        /**
+         * As an alternative, we can use a Singleton
+         * implementing an Observer pattern with
+         * Subscribers that will publish the triggered
+         * Domain Events into a queue system like
+         * Rabbit. It's useful for Legacy projects
+         * because you can trigger any Domain Event
+         * from any place in your code, not only
+         * Entities.
+         *
+         * DomainEventPublisher::getInstance()
+         *     ->notifyDomainEvent(
+         *         AuthorFollowed::fromFollow($this)
+         *     )
+         * );
+         */
+    }
+
+    public static function fromAuthorToAuthor(
+        FollowId $followId,
+        AuthorId $fromAuthorId,
+        AuthorId $toAuthorId,
+    ): static
+    {
+        return new static(
+            followId: $followId->toString(),
+            fromAuthorId: $fromAuthorId->toString(),
+            toAuthorId: $toAuthorId->toString()
         );
     }
+
+    public function fromAuthorId(): AuthorId
+    {
+        return AuthorId::fromString($this->fromAuthorId);
+    }
+
+    public function toAuthorId(): AuthorId
+    {
+        return AuthorId::fromString($this->toAuthorId);
+    }
+
+    public function followId(): FollowId
+    {
+        return FollowId::fromString($this->followId);
+    }
 }
+// end-snippet
\ No newline at end of file
diff --git a/src/Cheeper/Chapter7/DomainModel/Follow/Follows.php b/src/Cheeper/Chapter7/DomainModel/Follow/Follows.php
new file mode 100644
index 0000000..ece2349
--- /dev/null
+++ b/src/Cheeper/Chapter7/DomainModel/Follow/Follows.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\DomainModel\Follow;
+
+use Cheeper\DomainModel\Author\AuthorId;
+
+//snippet follows
+interface Follows
+{
+    public function numberOfFollowersFor(AuthorId $authorId): int;
+    public function add(Follow $follow): void;
+    public function ofFromAuthorIdAndToAuthorId(AuthorId $fromAuthorId, AuthorId $toAuthorId): ?Follow;
+    /** @return Follow[] */
+    public function toAuthorId(AuthorId $authorId): array;
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineMappings/Author.Author.orm.xml b/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineMappings/Author.Author.orm.xml
new file mode 100644
index 0000000..0cf17b2
--- /dev/null
+++ b/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineMappings/Author.Author.orm.xml
@@ -0,0 +1,19 @@
+<doctrine-mapping xmlns="http://doctrine-project.org/schemas/orm/doctrine-mapping"
+                  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+                  xsi:schemaLocation="http://doctrine-project.org/schemas/orm/doctrine-mapping
+                          https://www.doctrine-project.org/schemas/orm/doctrine-mapping.xsd">
+
+    <entity name="Cheeper\Chapter7\DomainModel\Author\Author" table="chapter7_authors">
+        <id name="authorId" type="string" column="author_id" length="36">
+            <generator strategy="NONE"/>
+        </id>
+
+        <field name="userName" column="user_name" length="255" />
+        <field name="email" column="email" length="255" />
+        <field name="name" column="name" length="100" nullable="true" />
+        <field name="biography" column="biography" type="text" nullable="true" />
+        <field name="location" column="location" length="100" nullable="true" />
+        <field name="website" column="website" length="100" nullable="true" />
+        <field name="birthDate" column="birth_date" type="date_immutable" nullable="true" />
+    </entity>
+</doctrine-mapping>
diff --git a/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineMappings/Cheep.Cheep.orm.xml b/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineMappings/Cheep.Cheep.orm.xml
new file mode 100644
index 0000000..a823bff
--- /dev/null
+++ b/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineMappings/Cheep.Cheep.orm.xml
@@ -0,0 +1,16 @@
+<doctrine-mapping xmlns="http://doctrine-project.org/schemas/orm/doctrine-mapping"
+                  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+                  xsi:schemaLocation="http://doctrine-project.org/schemas/orm/doctrine-mapping
+                          https://www.doctrine-project.org/schemas/orm/doctrine-mapping.xsd">
+
+    <entity name="Cheeper\Chapter7\DomainModel\Cheep\Cheep" table="chapter7_cheeps">
+        <id name="cheepId" column="cheep_id" type="string" length="36">
+            <generator strategy="NONE"/>
+        </id>
+
+        <embedded name="cheepMessage" class="Cheeper\DomainModel\Cheep\CheepMessage" />
+        <embedded name="cheepDate" class="Cheeper\DomainModel\Cheep\CheepDate" />
+
+        <field name="authorId" column="author_id" length="36" />
+    </entity>
+</doctrine-mapping>
diff --git a/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineMappings/Follow.Follow.orm.xml b/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineMappings/Follow.Follow.orm.xml
new file mode 100644
index 0000000..9000288
--- /dev/null
+++ b/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineMappings/Follow.Follow.orm.xml
@@ -0,0 +1,14 @@
+<doctrine-mapping xmlns="http://doctrine-project.org/schemas/orm/doctrine-mapping"
+                  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+                  xsi:schemaLocation="http://doctrine-project.org/schemas/orm/doctrine-mapping
+                          https://www.doctrine-project.org/schemas/orm/doctrine-mapping.xsd">
+
+    <entity name="Cheeper\Chapter7\DomainModel\Follow\Follow" table="chapter7_follows">
+        <id name="followId" type="string" column="follow_id" length="36">
+            <generator strategy="NONE"/>
+        </id>
+
+        <field name="fromAuthorId" column="from_author_id" length="36" />
+        <field name="toAuthorId" column="to_author_id" length="36" />
+    </entity>
+</doctrine-mapping>
diff --git a/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineOrmAuthors.php b/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineOrmAuthors.php
new file mode 100644
index 0000000..ee8bb8f
--- /dev/null
+++ b/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineOrmAuthors.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Infrastructure\Persistence;
+
+use Cheeper\Chapter7\DomainModel\Author\Author;
+use Cheeper\Chapter7\DomainModel\Author\Authors;
+use Cheeper\DomainModel\Author\AuthorId;
+use Cheeper\DomainModel\Author\UserName;
+use Doctrine\ORM\EntityManagerInterface;
+
+//snippet doctrine-orm-authors
+final class DoctrineOrmAuthors implements Authors
+{
+    public function __construct(
+        private EntityManagerInterface $em
+    ) {
+    }
+
+    public function ofId(AuthorId $authorId): ?Author
+    {
+        return $this->em
+            ->getRepository(Author::class)
+            ->findOneBy([
+                'authorId' => $authorId->id(),
+            ]);
+    }
+
+    public function ofUserName(UserName $userName): ?Author
+    {
+        return $this->em
+            ->getRepository(Author::class)
+            ->findOneBy(['userName' => $userName->userName()]);
+    }
+
+    public function add(Author $author): void
+    {
+        $this->em->persist($author);
+    }
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineOrmCheeps.php b/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineOrmCheeps.php
new file mode 100644
index 0000000..d5de767
--- /dev/null
+++ b/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineOrmCheeps.php
@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Infrastructure\Persistence;
+
+use Cheeper\Chapter7\DomainModel\Cheep\Cheep;
+use Cheeper\Chapter7\DomainModel\Cheep\Cheeps;
+use Cheeper\DomainModel\Cheep\CheepId;
+use Doctrine\ORM\EntityManagerInterface;
+use Ramsey\Uuid\Uuid;
+
+//snippet doctrine-orm-cheeps
+final class DoctrineOrmCheeps implements Cheeps
+{
+    //ignore
+    public function __construct(
+        private EntityManagerInterface $em
+    ) {
+    }
+
+    public function add(Cheep $cheep): void
+    {
+        $this->em->persist($cheep);
+    }
+    //end-ignore
+
+    public function ofId(CheepId $cheepId): ?Cheep
+    {
+        return $this->em->find(Cheep::class, Uuid::fromString($cheepId->id()));
+    }
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineOrmFollows.php b/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineOrmFollows.php
new file mode 100644
index 0000000..c03b2ec
--- /dev/null
+++ b/src/Cheeper/Chapter7/Infrastructure/Persistence/DoctrineOrmFollows.php
@@ -0,0 +1,49 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Infrastructure\Persistence;
+
+use Cheeper\Chapter7\DomainModel\Follow\Follow;
+use Cheeper\Chapter7\DomainModel\Follow\Follows;
+use Cheeper\DomainModel\Author\AuthorId;
+use Doctrine\ORM\EntityManagerInterface;
+use Doctrine\ORM\EntityRepository;
+use Doctrine\Persistence\ObjectRepository;
+
+//snippet doctrine-orm-follows
+final class DoctrineOrmFollows implements Follows
+{
+    public function __construct(
+        private EntityManagerInterface $em
+    ) {
+    }
+
+    public function numberOfFollowersFor(AuthorId $authorId): int
+    {
+        return 13;
+    }
+
+    public function add(Follow $follow): void
+    {
+        $this->em->persist($follow);
+    }
+
+    public function ofFromAuthorIdAndToAuthorId(AuthorId $fromAuthorId, AuthorId $toAuthorId): ?Follow
+    {
+        $repository = $this->em->getRepository(Follow::class);
+
+        return $repository->findOneBy([
+            'fromAuthorId' => $fromAuthorId,
+            'toAuthorId' => $toAuthorId,
+        ]);
+    }
+
+    public function toAuthorId(AuthorId $authorId): array
+    {
+        $repository = $this->em->getRepository(Follow::class);
+
+        return $repository->findBy(['toAuthorId' => $authorId]);
+    }
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter7/Infrastructure/Persistence/InMemoryAuthors.php b/src/Cheeper/Chapter7/Infrastructure/Persistence/InMemoryAuthors.php
new file mode 100644
index 0000000..dc97c54
--- /dev/null
+++ b/src/Cheeper/Chapter7/Infrastructure/Persistence/InMemoryAuthors.php
@@ -0,0 +1,59 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Infrastructure\Persistence;
+
+use Cheeper\Chapter7\DomainModel\Author\Author;
+use Cheeper\Chapter7\DomainModel\Author\Authors;
+use Cheeper\DomainModel\Author\AuthorId;
+use Cheeper\DomainModel\Author\UserName;
+use function Functional\head;
+use function Functional\select;
+
+final class InMemoryAuthors implements Authors
+{
+    public array $authors;
+
+    public function __construct()
+    {
+        $this->authors = [];
+    }
+
+    public function ofId(AuthorId $authorId): ?Author
+    {
+        $candidate = head(
+            select($this->authors, fn (Author $u): bool => $u->authorId()->equals($authorId))
+        );
+
+        if (null === $candidate) {
+            return $candidate;
+        }
+
+        return $candidate;
+    }
+
+    public function ofUserName(UserName $userName): ?Author
+    {
+        $candidate = head(
+            select($this->authors, fn (Author $u): bool => $u->userName()->equalsTo($userName))
+        );
+
+        if (null === $candidate) {
+            return null;
+        }
+
+        return $candidate;
+    }
+
+    public function add(Author $author): void
+    {
+        $candidate = head(
+            select($this->authors, fn (Author $u): bool => $u->authorId()->equals($author->authorId()))
+        );
+
+        if ((null !== $candidate && $candidate !== $author) || null === $candidate) {
+            $this->authors[$author->authorId()->toString()] = $author;
+        }
+    }
+}
diff --git a/src/Cheeper/Chapter7/Infrastructure/Persistence/InMemoryCheeps.php b/src/Cheeper/Chapter7/Infrastructure/Persistence/InMemoryCheeps.php
new file mode 100644
index 0000000..042062e
--- /dev/null
+++ b/src/Cheeper/Chapter7/Infrastructure/Persistence/InMemoryCheeps.php
@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Infrastructure\Persistence;
+
+use Cheeper\Chapter7\DomainModel\Cheep\Cheep;
+use Cheeper\Chapter7\DomainModel\Cheep\Cheeps;
+use Cheeper\DomainModel\Cheep\CheepId;
+
+//snippet inmemory-cheeps
+final class InMemoryCheeps implements Cheeps
+{
+    /** @var Cheep[] */
+    private array $items = [];
+
+    public function add(Cheep $cheep): void
+    {
+        $this->items[$cheep->cheepId()->toString()] = $cheep;
+    }
+
+    public function ofId(CheepId $cheepId): ?Cheep
+    {
+        return $this->items[$cheepId->toString()] ?? null;
+    }
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter7/Infrastructure/Persistence/InMemoryFollows.php b/src/Cheeper/Chapter7/Infrastructure/Persistence/InMemoryFollows.php
new file mode 100644
index 0000000..b621da8
--- /dev/null
+++ b/src/Cheeper/Chapter7/Infrastructure/Persistence/InMemoryFollows.php
@@ -0,0 +1,68 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Infrastructure\Persistence;
+
+use Cheeper\Chapter7\DomainModel\Follow\Follow;
+use Cheeper\Chapter7\DomainModel\Follow\Follows;
+use Cheeper\DomainModel\Author\AuthorId;
+use Cheeper\DomainModel\Follow\FollowId;
+use function Functional\head;
+use function Functional\reduce_left;
+use function Functional\select;
+
+final class InMemoryFollows implements Follows
+{
+    /** @var array<string, Follow> */
+    public array $collection = [];
+
+    public function ofId(FollowId $followId): ?Follow
+    {
+        $candidate = head(
+            select($this->collection, fn (Follow $u): bool => $u->followId()->equals($followId))
+        );
+
+        if (null === $candidate) {
+            return null;
+        }
+
+        return $candidate;
+    }
+
+    public function add(Follow $follow): void
+    {
+        $candidate = head(
+            select($this->collection, fn (Follow $u): bool => $u->fromAuthorId()->equals($follow->fromAuthorId()) && $u->toAuthorId()->equals($follow->toAuthorId()))
+        );
+
+        if ((null !== $candidate && $candidate != $follow) || null === $candidate) {
+            $this->collection[$follow->followId()->toString()] = $follow;
+        }
+    }
+
+    public function numberOfFollowersFor(AuthorId $authorId): int
+    {
+        return reduce_left(
+            $this->collection,
+            function(Follow $f, string $key, array $collection, int $initial) use($authorId): int {
+                return $initial + ($f->fromAuthorId()->equals($authorId) ? 1 : 0);
+            },
+            0
+        );
+    }
+
+    public function ofFromAuthorIdAndToAuthorId(AuthorId $fromAuthorId, AuthorId $toAuthorId): ?Follow
+    {
+        $candidate = head(
+            select($this->collection, fn (Follow $u): bool => $u->fromAuthorId()->equals($fromAuthorId) && $u->toAuthorId()->equals($toAuthorId))
+        );
+
+        return $candidate ?? null;
+    }
+
+    public function toAuthorId(AuthorId $authorId): array
+    {
+        return select($this->collection, fn (Follow $f): bool => $f->toAuthorId()->equals($authorId));
+    }
+}
diff --git a/src/Cheeper/DomainModel/Author/Author.php b/src/Cheeper/DomainModel/Author/Author.php
index 29531e3..db619ea 100644
--- a/src/Cheeper/DomainModel/Author/Author.php
+++ b/src/Cheeper/DomainModel/Author/Author.php
@@ -8,8 +8,9 @@ use Cheeper\DomainModel\Follow\Follow;
 use Cheeper\DomainModel\Follow\FollowId;
 use Cheeper\DomainModel\TriggerEventsTrait;
 use DateTimeImmutable;
+use InvalidArgumentException;
 
-class Author
+final class Author
 {
     use TriggerEventsTrait;
 
@@ -28,10 +29,15 @@ class Author
         $this->setLocation($location);
 
         $this->notifyDomainEvent(
-            NewAuthorSigned::fromAuthor($this)
+            $this->buildNewAuthorSignedDomainEvent()
         );
     }
 
+    protected function buildNewAuthorSignedDomainEvent(): NewAuthorSigned
+    {
+        return NewAuthorSigned::fromAuthor($this);
+    }
+
     public static function signUp(
         AuthorId $authorId,
         UserName $userName,
@@ -126,7 +132,7 @@ class Author
     private function checkIsNotNull(?string $value, string $errorMessage): ?string
     {
         if ('' === $value) {
-            throw new \InvalidArgumentException($errorMessage);
+            throw new InvalidArgumentException($errorMessage);
         }
 
         return $value;
diff --git a/src/Cheeper/DomainModel/Author/NewAuthorSigned.php b/src/Cheeper/DomainModel/Author/NewAuthorSigned.php
index 800f32f..93a9443 100644
--- a/src/Cheeper/DomainModel/Author/NewAuthorSigned.php
+++ b/src/Cheeper/DomainModel/Author/NewAuthorSigned.php
@@ -17,9 +17,9 @@ class NewAuthorSigned implements DomainEvent
     ) {
     }
 
-    public static function fromAuthor(Author $author): self
+    public static function fromAuthor(Author $author): static
     {
-        return new self(
+        return new static(
             $author->authorId()->toString(),
             new DateTimeImmutable(
                 timezone: new DateTimeZone("UTC")
diff --git a/tests/Cheeper/Tests/Chapter7/Application/Command/Author/FollowHandlerTest.php b/tests/Cheeper/Tests/Chapter7/Application/Command/Author/FollowHandlerTest.php
index aa50f3d..1d6e831 100644
--- a/tests/Cheeper/Tests/Chapter7/Application/Command/Author/FollowHandlerTest.php
+++ b/tests/Cheeper/Tests/Chapter7/Application/Command/Author/FollowHandlerTest.php
@@ -4,11 +4,15 @@ declare(strict_types=1);
 
 namespace Cheeper\Tests\Chapter7\Application\Command\Author;
 
+use Cheeper\Chapter6\Infrastructure\Application\Event\InMemoryEventBus;
 use Cheeper\Chapter7\Application\Command\Author\FollowHandler;
 use Cheeper\Chapter7\Application\Command\Author\Follow;
 use Cheeper\Chapter7\DomainModel\Author\Author;
+use Cheeper\Chapter7\DomainModel\Follow\Follow as FollowRelation;
 use Cheeper\Chapter7\DomainModel\Follow\AuthorFollowed;
-use Cheeper\DomainModel\Follow\Follow as FollowRelation;
+use Cheeper\Chapter7\Infrastructure\Persistence\InMemoryAuthors;
+use Cheeper\Chapter7\Infrastructure\Persistence\InMemoryFollows;
+
 use Cheeper\DomainModel\Author\AuthorDoesNotExist;
 use Cheeper\DomainModel\Author\AuthorId;
 use Cheeper\DomainModel\Follow\FollowId;
@@ -19,8 +23,7 @@ use PHPUnit\Framework\TestCase;
 
 final class FollowHandlerTest extends TestCase
 {
-    use SendsCommands;
-
+    private const FOLLOW_ID = '337df284-d475-4cbd-89af-12d7451f73f1';
     private const AUTHOR_ID_FROM = '400ea77d-0c8c-44f2-abe8-db05d0852966';
     private const AUTHOR_ID_TO = '52d8f0b5-544f-46e0-84dc-f8b513391a0e';
 
@@ -29,12 +32,23 @@ final class FollowHandlerTest extends TestCase
     private const EMAIL_KEYVAN = 'keyvan.akbary@gmail.com';
     private const EMAIL_CARLOS = 'carlos.buenosvinos@gmail.com';
 
+    protected function setUp(): void
+    {
+        $this->authors = new InMemoryAuthors();
+        $this->follows = new InMemoryFollows();
+        $this->eventBus = new InMemoryEventBus();
+    }
+
     /** @test */
     public function givenTwoNonExistingAuthorsWhenFollowingOneToAnotherOneNonExistingAuthorExceptionShouldBeThrown(): void
     {
         $this->expectException(AuthorDoesNotExist::class);
 
-        $this->runHandler(self::AUTHOR_ID_FROM, self::AUTHOR_ID_TO);
+        $this->runHandler(
+            self::FOLLOW_ID,
+            self::AUTHOR_ID_FROM,
+            self::AUTHOR_ID_TO
+        );
     }
 
     /** @test */
@@ -50,7 +64,11 @@ final class FollowHandlerTest extends TestCase
             )
         );
 
-        $this->runHandler(self::AUTHOR_ID_FROM, self::AUTHOR_ID_TO);
+        $this->runHandler(
+            self::FOLLOW_ID,
+            self::AUTHOR_ID_FROM,
+            self::AUTHOR_ID_TO
+        );
     }
 
     /** @test */
@@ -66,7 +84,11 @@ final class FollowHandlerTest extends TestCase
             )
         );
 
-        $this->runHandler(self::AUTHOR_ID_FROM, self::AUTHOR_ID_TO);
+        $this->runHandler(
+            self::FOLLOW_ID,
+            self::AUTHOR_ID_FROM,
+            self::AUTHOR_ID_TO
+        );
     }
 
     /** @test */
@@ -74,7 +96,6 @@ final class FollowHandlerTest extends TestCase
     {
         $fromAuthorId = self::AUTHOR_ID_FROM;
         $toAuthorId = self::AUTHOR_ID_TO;
-        $followId = '51d8ffff-123f-78e1-48fc-f8b513391a0e';
 
         $fromAuthor = Author::signUp(
             AuthorId::fromString($fromAuthorId),
@@ -90,15 +111,20 @@ final class FollowHandlerTest extends TestCase
 
         $this->authors->add($fromAuthor);
         $this->authors->add($toAuthor);
+
         $this->follows->add(
             FollowRelation::fromAuthorToAuthor(
-                FollowId::fromString($followId),
+                FollowId::fromString(self::FOLLOW_ID),
                 $fromAuthor->authorId(),
                 $toAuthor->authorId(),
             )
         );
 
-        $this->runHandler($fromAuthorId, $toAuthorId);
+        $this->runHandler(
+            self::FOLLOW_ID,
+            self::AUTHOR_ID_FROM,
+            self::AUTHOR_ID_TO
+        );
 
         $this->assertCount(
             1,
@@ -130,7 +156,11 @@ final class FollowHandlerTest extends TestCase
         $this->authors->add($fromAuthor);
         $this->authors->add($toAuthor);
 
-        $command = $this->runHandler($fromAuthorId, $toAuthorId);
+        $command = $this->runHandler(
+            self::FOLLOW_ID,
+            $fromAuthorId,
+            $toAuthorId
+        );
 
         $this->assertCount(
             1,
@@ -155,14 +185,19 @@ final class FollowHandlerTest extends TestCase
         );
     }
 
-    private function runHandler(string $fromAuthorId, string $toAuthorId): Follow
+    private function runHandler(
+        string $followId,
+        string $fromAuthorId,
+        string $toAuthorId
+    ): Follow
     {
         $this->eventBus->reset();
 
-        $command = (Follow::fromAuthorIdToAuthorId(
-            $fromAuthorId,
-            $toAuthorId
-        ))->stampAsNewMessage();
+        $command = Follow::fromArray([
+            'follow_id' => $followId,
+            'from_author_id' => $fromAuthorId,
+            'to_author_id' => $toAuthorId
+        ]);
 
         (new FollowHandler(
             $this->authors,