add Comment persistence: model, migration, eloquent + fake repo

backend/app/Comment/EloquentCommentRepository.php

@@ -0,0 +1,66 @@
+<?php
+
+namespace App\Comment;
+
+use DateTimeImmutable;
+use DateTimeZone;
+
+class EloquentCommentRepository implements CommentRepository
+{
+    public function create(CreateCommentDto $dto): Comment
+    {
+        $model = CommentModel::create([
+            'post_id' => $dto->postId,
+            'user_id' => $dto->userId,
+            'body' => $dto->body,
+            'created_at' => $dto->createdAt,
+        ]);
+
+        return $this->toDomain($model);
+    }
+
+    public function find(int $id): ?Comment
+    {
+        $model = CommentModel::find($id);
+
+        return $model === null ? null : $this->toDomain($model);
+    }
+
+    /**
+     * @return Comment[]
+     */
+    public function findByPostId(int $postId): array
+    {
+        $models = CommentModel::query()
+            ->where('post_id', $postId)
+            ->orderBy('created_at', 'asc')
+            ->get();
+
+        return $models->map(
+            function (CommentModel $model) {
+                return $this->toDomain($model);
+            },
+        )->all();
+    }
+
+    public function delete(int $id): void
+    {
+        CommentModel::query()->where('id', $id)->delete();
+    }
+
+    private function toDomain(CommentModel $model): Comment
+    {
+        $utc = new DateTimeZone('UTC');
+
+        return new Comment(
+            id: $model->id,
+            postId: $model->post_id,
+            userId: $model->user_id,
+            body: $model->body,
+            createdAt: new DateTimeImmutable(
+                $model->created_at->toDateTimeString(),
+                $utc,
+            ),
+        );
+    }
+}