Fix finding resource when creating polymorphic relationship

Previously the relationship's collection was responsible for finding the
resource by ID, but this discarded the provided type information. Now
the resource itself is responsible for finding the resource, and the
collection merely specifies which resources are allowed in the
relationship.

Fixes #93

Author: tobyzerner

src/Schema/Field/Relationship.php

@@ -74,18 +74,18 @@ protected function findResourceForIdentifier(array $identifier, Context $context
             throw new BadRequestException('id not specified');
         }
 
-        $collections = array_map(
-            fn($collection) => $context->api->getCollection($collection),
-            $this->collections,
+        $resources = array_merge(
+            ...array_map(
+                fn($collection) => $context->api->getCollection($collection)->resources(),
+                $this->collections,
+            ),
         );
 
-        foreach ($collections as $collection) {
-            if (in_array($identifier['type'], $collection->resources())) {
-                return $this->findResource(
-                    $context->withCollection($collection),
-                    $identifier['id'],
-                );
-            }
+        if (in_array($identifier['type'], $resources)) {
+            return $this->findResource(
+                $context->withCollection($context->resource($identifier['type'])),
+                $identifier['id'],
+            );
         }
 
         throw (new BadRequestException("type [{$identifier['type']}] not allowed"))->setSource([

tests/feature/RelationshipToOneTest.php

@@ -2,14 +2,14 @@
 
 namespace Tobyz\Tests\JsonApiServer\feature;
 
-use stdClass;
 use Tobyz\JsonApiServer\Endpoint\Create;
 use Tobyz\JsonApiServer\Endpoint\Show;
 use Tobyz\JsonApiServer\Exception\BadRequestException;
 use Tobyz\JsonApiServer\Exception\UnprocessableEntityException;
 use Tobyz\JsonApiServer\JsonApi;
 use Tobyz\JsonApiServer\Schema\Field\ToOne;
 use Tobyz\Tests\JsonApiServer\AbstractTestCase;
+use Tobyz\Tests\JsonApiServer\MockCollection;
 use Tobyz\Tests\JsonApiServer\MockResource;
 
 class RelationshipToOneTest extends AbstractTestCase
@@ -213,16 +213,18 @@ public function test_to_one_create_invalid_type()
 
     public function test_to_one_create_polymorphic()
     {
-        $this->api->resource(new MockResource('animals', models: [(object) ['id' => '1']]));
+        $this->api->resource(
+            new MockResource('animals', models: [($friend = (object) ['id' => '1'])]),
+        );
 
         $this->api->resource(
-            new MockResource(
+            $resource = new MockResource(
                 'users',
                 models: [(object) ['id' => '1']],
                 endpoints: [Create::make()],
                 fields: [
                     ToOne::make('friend')
-                        ->type(['users', stdClass::class => 'animals'])
+                        ->type(['users', 'animals'])
                         ->writable(),
                 ],
             ),
@@ -238,6 +240,44 @@ public function test_to_one_create_polymorphic()
         );
 
         $this->assertEquals(201, $response->getStatusCode());
+        $this->assertSame($friend, $resource->models[1]->friend);
+    }
+
+    public function test_to_one_create_collection()
+    {
+        $this->api->collection(
+            new MockCollection('animals', [
+                'dogs' => [(object) ['id' => '1']],
+                'cats' => [($cat = (object) ['id' => '1'])],
+            ]),
+        );
+
+        $this->api->resource(new MockResource('cats', models: [$cat]));
+
+        $this->api->resource(
+            $resource = new MockResource(
+                'users',
+                models: [(object) ['id' => '1']],
+                endpoints: [Create::make()],
+                fields: [
+                    ToOne::make('pet')
+                        ->collection('animals')
+                        ->writable(),
+                ],
+            ),
+        );
+
+        $response = $this->api->handle(
+            $this->buildRequest('POST', '/users')->withParsedBody([
+                'data' => [
+                    'type' => 'users',
+                    'relationships' => ['pet' => ['data' => ['type' => 'cats', 'id' => '1']]],
+                ],
+            ]),
+        );
+
+        $this->assertEquals(201, $response->getStatusCode());
+        $this->assertSame($cat, $resource->models[1]->pet);
     }
 
     public function test_to_one_create_null_not_nullable()