Fix support for nested includes on polymorphic relationship

Closes #99

Author: tobyzerner

src/Endpoint/Concerns/IncludesData.php

@@ -76,10 +76,16 @@ private function validateInclude(
                     continue;
                 }
 
-                $types = $field->collections;
-
-                $relatedResources = $types
-                    ? array_map(fn($type) => $context->api->getResource($type), $types)
+                $relatedResources = $field->collections
+                    ? array_merge(
+                        ...array_map(
+                            fn($collection) => array_map(
+                                fn($resource) => $context->api->getResource($resource),
+                                $context->api->getCollection($collection)->resources(),
+                            ),
+                            $field->collections,
+                        ),
+                    )
                     : array_values($context->api->resources);
 
                 $this->validateInclude($context, $relatedResources, $nested, $name . '.');

tests/specification/InclusionOfRelatedResourcesTest.php

@@ -9,6 +9,7 @@
 use Tobyz\JsonApiServer\Schema\Field\ToMany;
 use Tobyz\JsonApiServer\Schema\Field\ToOne;
 use Tobyz\Tests\JsonApiServer\AbstractTestCase;
+use Tobyz\Tests\JsonApiServer\MockCollection;
 use Tobyz\Tests\JsonApiServer\MockResource;
 
 /**
@@ -182,4 +183,92 @@ public function test_relationship_inclusion_on_list_endpoint()
             $response->getBody(),
         );
     }
+
+    public function test_relationship_inclusion_for_polymorphic_relationship()
+    {
+        $api = new JsonApi();
+
+        $api->resource(
+            new MockResource(
+                'users',
+                models: [($user1 = (object) ['id' => '1', 'name' => 'Toby'])],
+                fields: [Attribute::make('name')],
+            ),
+        );
+
+        $api->resource(
+            new MockResource(
+                'posts',
+                models: [($post1 = (object) ['id' => '1', 'author' => $user1])],
+                fields: [
+                    ToOne::make('author')
+                        ->type('users')
+                        ->includable(),
+                ],
+            ),
+        );
+
+        $api->collection(
+            new MockCollection('subjects', [
+                'users' => [$user1],
+                'posts' => [$post1],
+            ]),
+        );
+
+        $api->resource(
+            new MockResource(
+                'notifications',
+                models: [
+                    ((object) ['id' => '1', 'subject' => $post1]),
+                    ((object) ['id' => '2', 'subject' => $user1]),
+                ],
+                endpoints: [Index::make()],
+                fields: [
+                    ToOne::make('subject')
+                        ->collection('subjects')
+                        ->includable(),
+                ],
+            ),
+        );
+
+        $response = $api->handle(
+            $this->buildRequest('GET', '/notifications?include=subject.author'),
+        );
+
+        $this->assertJsonApiDocumentSubset(
+            [
+                'data' => [
+                    [
+                        'type' => 'notifications',
+                        'id' => '1',
+                        'relationships' => [
+                            'subject' => [
+                                'data' => ['type' => 'posts', 'id' => '1'],
+                            ],
+                        ],
+                    ],
+                    [
+                        'type' => 'notifications',
+                        'id' => '2',
+                        'relationships' => [
+                            'subject' => [
+                                'data' => ['type' => 'users', 'id' => '1'],
+                            ],
+                        ],
+                    ],
+                ],
+                'included' => [
+                    [
+                        'type' => 'posts',
+                        'id' => '1',
+                    ],
+                    [
+                        'type' => 'users',
+                        'id' => '1',
+                    ],
+                ],
+            ],
+            $response->getBody(),
+        );
+    }
 }