add element child list

backend/app/Controllers/ElementController.php

@@ -17,7 +17,7 @@ class ElementController
     public function show(?int $id): JsonResponse
     {
         try {
-            $element = $this->getElement->execute(
+            $result = $this->getElement->execute(
                 new GetElementRequest(id: $id)
             );
         } catch (BadRequestException $exception) {
@@ -30,7 +30,17 @@ class ElementController
             ], 404);
         }
 
+        $element = $result->getElement();
+        $childElements = [];
+        foreach ($result->getChildElements() as $childElement) {
+            $childElements[] = [
+                'id' => $childElement->getId(),
+                'title' => $childElement->getTitle(),
+            ];
+        }
+
         return new JsonResponse([
+            'childElements' => $childElements,
             'element' => [
                 'id' => $element->getId(),
                 'title' => $element->getTitle(),

backend/app/Element/ElementRepository.php

@@ -16,4 +16,9 @@ interface ElementRepository
      * @return Element[]
      */
     public function findBySet(DomainSet $set): array;
+
+    /**
+     * @return Element[]
+     */
+    public function findByParentElement(Element $parentElement): array;
 }

backend/app/Element/EloquentElementRepository.php

@@ -61,6 +61,25 @@ class EloquentElementRepository implements ElementRepository
         return $elements;
     }
 
+    /**
+     * @return Element[]
+     */
+    public function findByParentElement(Element $parentElement): array
+    {
+        $models = ElementModel::where(
+            'parent_element_id',
+            $parentElement->getId(),
+        )
+            ->orderBy('id')
+            ->get();
+        $elements = [];
+        foreach ($models as $model) {
+            $elements[] = $this->toDomain($model);
+        }
+
+        return $elements;
+    }
+
     private function toDomain(ElementModel $model): Element
     {
         $set = $this->setRepo->find($model->set_id);

backend/app/Element/UseCases/GetElement/GetElement.php

@@ -2,7 +2,6 @@
 
 namespace App\Element\UseCases\GetElement;
 
-use App\Element\Element;
 use App\Element\ElementRepository;
 use App\Exceptions\BadRequestException;
 use App\Exceptions\NotFoundException;
@@ -17,7 +16,7 @@ class GetElement
      * @throws BadRequestException
      * @throws NotFoundException
      */
-    public function execute(GetElementRequest $request): Element
+    public function execute(GetElementRequest $request): GetElementResult
     {
         if ($request->id === null) {
             throw new BadRequestException('id is required');
@@ -28,6 +27,10 @@ class GetElement
             throw new NotFoundException('Element not found');
         }
 
-        return $element;
+        return new GetElementResult(
+            element: $element,
+            childElements: $this->elementRepository
+                ->findByParentElement($element),
+        );
     }
 }

backend/app/Element/UseCases/GetElement/GetElementResult.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace App\Element\UseCases\GetElement;
+
+use App\Element\Element;
+
+class GetElementResult
+{
+    /**
+     * @param Element[] $childElements
+     */
+    public function __construct(
+        private Element $element,
+        private array $childElements,
+    ) {
+    }
+
+    public function getElement(): Element
+    {
+        return $this->element;
+    }
+
+    /**
+     * @return Element[]
+     */
+    public function getChildElements(): array
+    {
+        return $this->childElements;
+    }
+}