fix(laravel): persist HasMany and MorphMany relationships

src/Laravel/Eloquent/State/PersistProcessor.php

@@ -18,6 +18,7 @@
 use ApiPlatform\Metadata\HttpOperation;
 use ApiPlatform\Metadata\Operation;
 use ApiPlatform\State\ProcessorInterface;
+use Illuminate\Database\Eloquent\Collection;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
 use Illuminate\Database\Eloquent\Relations\HasMany;
 use Illuminate\Database\Eloquent\Relations\MorphMany;
@@ -62,7 +63,7 @@ public function process(mixed $data, Operation $operation, array $uriVariables =
             if (HasMany::class === $relation['type'] || MorphMany::class === $relation['type']) {
                 $rel = $data->{$relation['name']};
 
-                if (!\is_array($rel)) {
+                if (!\is_array($rel) && !$rel instanceof Collection) {
                     throw new RuntimeException('To-Many relationship is not a collection.');
                 }
 

src/Laravel/Tests/EloquentTest.php

@@ -523,4 +523,19 @@ public function testRelationIsHandledOnCreateWithNestedDataToMany(): void
             ],
         ]);
     }
+
+    public function testPostWithEmptyMorphMany(): void
+    {
+        $response = $this->postJson('/api/post_with_morph_manies', [
+            'title' => 'My first post',
+            'content' => 'This is the content of my first post.',
+            'comments' => [['content' => 'hello']],
+        ], ['accept' => 'application/ld+json', 'content-type' => 'application/ld+json']);
+        $response->assertStatus(201);
+        $response->assertJson([
+            'title' => 'My first post',
+            'content' => 'This is the content of my first post.',
+            'comments' => [['content' => 'hello']],
+        ]);
+    }
 }

src/Laravel/workbench/app/Models/CommentMorph.php

@@ -0,0 +1,33 @@
+<?php
+
+/*
+ * This file is part of the API Platform project.
+ *
+ * (c) Kévin Dunglas <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace Workbench\App\Models;
+
+use ApiPlatform\Metadata\ApiProperty;
+use ApiPlatform\Metadata\NotExposed;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\MorphTo;
+use Symfony\Component\Serializer\Attribute\Groups;
+
+#[NotExposed]
+#[ApiProperty(serialize: new Groups(['comments']), property: 'content')]
+class CommentMorph extends Model
+{
+    protected $table = 'comments_morph';
+    protected $fillable = ['content'];
+
+    public function commentable(): MorphTo
+    {
+        return $this->morphTo();
+    }
+}

src/Laravel/workbench/app/Models/PostWithMorphMany.php

@@ -0,0 +1,41 @@
+<?php
+
+/*
+ * This file is part of the API Platform project.
+ *
+ * (c) Kévin Dunglas <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace Workbench\App\Models;
+
+use ApiPlatform\Metadata\ApiProperty;
+use ApiPlatform\Metadata\ApiResource;
+use ApiPlatform\Metadata\Post;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\MorphMany;
+use Symfony\Component\Serializer\Attribute\Groups;
+
+#[ApiResource(operations: [
+    new Post(
+        denormalizationContext: ['groups' => ['comments']],
+        normalizationContext: ['groups' => ['comments']],
+    ),
+])]
+#[ApiProperty(serialize: new Groups(['comments']), property: 'title')]
+#[ApiProperty(serialize: new Groups(['comments']), property: 'content')]
+#[ApiProperty(serialize: new Groups(['comments']), property: 'comments')]
+class PostWithMorphMany extends Model
+{
+    protected $table = 'posts_with_morph_many';
+    protected $fillable = ['title', 'content'];
+
+    public function comments(): MorphMany
+    {
+        return $this->morphMany(CommentMorph::class, 'commentable');
+    }
+}

src/Laravel/workbench/database/migrations/2025_06_13_130000_create_posts_with_morph_many_table.php

@@ -0,0 +1,41 @@
+<?php
+
+/*
+ * This file is part of the API Platform project.
+ *
+ * (c) Kévin Dunglas <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration {
+    public function up(): void
+    {
+        Schema::create('posts_with_morph_many', function (Blueprint $table): void {
+            $table->id();
+            $table->string('title');
+            $table->text('content');
+            $table->timestamps();
+        });
+
+        Schema::create('comments_morph', function (Blueprint $table): void {
+            $table->id();
+            $table->text('content');
+            $table->morphs('commentable');
+            $table->timestamps();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('posts_with_morph_many');
+        Schema::dropIfExists('comments_morph');
+    }
+};