Update getMediaBuilder method

src/Block/MediaBlockService.php

@@ -93,7 +93,7 @@ public function configureEditForm(FormMapper $form, BlockInterface $block): void
                     'label' => 'form.label_class',
                     'required' => false,
                 ]],
-                [$this->getMediaBuilder(), null, []],
+                [$this->getMediaBuilder($form), null, []],
                 ['format', ChoiceType::class, [
                     'required' => \count($formatChoices) > 0,
                     'choices' => $formatChoices,
@@ -195,7 +195,10 @@ private function getFormatChoices(?MediaInterface $media = null): array
         return $formatChoices;
     }
 
-    private function getMediaBuilder(): FormBuilderInterface
+    /**
+     * @param AdminFormMapper<object> $form
+     */
+    private function getMediaBuilder(FormMapper $form): FormBuilderInterface
     {
         if (null === $this->mediaAdmin) {
             throw new \LogicException('The SonataAdminBundle is required to render the edit form.');
@@ -208,14 +211,17 @@ private function getMediaBuilder(): FormBuilderInterface
 
         $fieldDescription->setAssociationAdmin($this->mediaAdmin);
 
-        $formBuilder = $this->mediaAdmin->getFormBuilder()->create('mediaId', ModelListType::class, [
+        $formBuilder = $form->getFormBuilder()->create('mediaId', ModelListType::class, [
             'sonata_field_description' => $fieldDescription,
             'class' => $this->mediaAdmin->getClass(),
             'model_manager' => $this->mediaAdmin->getModelManager(),
             'label' => 'form.label_media',
         ]);
 
-        // Add ModelTransformer ?
+        $formBuilder->addModelTransformer(new CallbackTransformer(
+            static fn (mixed $value): ?PageBlockInterface => $value,
+            static fn (?PageBlockInterface $value) => $value instanceof PageBlockInterface ? $value->getId() : $value
+        ));
 
         return $formBuilder;
     }