[JSON:API] Supports JsonApiResource::toRelationships()

src/Illuminate/Http/Resources/JsonApi/AnonymousResourceCollection.php

@@ -20,7 +20,6 @@ public function with($request)
             'included' => $this->collection
                 ->map(fn ($resource) => $resource->resolveIncludedResources($request))
                 ->flatten(depth: 1)
-                ->uniqueStrict(fn ($relation): array => [$relation['id'], $relation['type']])
                 ->all(),
             ...($implementation = JsonApiResource::$jsonApiInformation)
                 ? ['jsonapi' => $implementation]

src/Illuminate/Http/Resources/JsonApi/Concerns/ResolvesJsonApiElements.php

@@ -4,6 +4,9 @@
 
 use Illuminate\Contracts\Support\Arrayable;
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\AsPivot;
+use Illuminate\Database\Eloquent\Relations\BelongsToMany;
+use Illuminate\Database\Eloquent\Relations\Pivot;
 use Illuminate\Database\Eloquent\Relations\Relation;
 use Illuminate\Http\Request;
 use Illuminate\Http\Resources\Json\JsonResource;
@@ -138,6 +141,8 @@ protected function compileResourceRelationships(Request $request): void
             return;
         }
 
+        $this->resource->loadMissing($this->toRelationships($request));
+
         $this->loadedRelationshipsMap = new WeakMap;
 
         $this->loadedRelationshipIdentifiers = (new Collection($this->resource->getRelations()))
@@ -147,55 +152,70 @@ protected function compileResourceRelationships(Request $request): void
                         return [$key => ['data' => $relations]];
                     }
 
+                    $relationship = $this->resource->{$key}();
+
+                    $isUnique = ! $relationship instanceof BelongsToMany;
+
                     $key = static::resourceTypeFromModel($relations->first());
 
-                    return [$key => ['data' => $relations->map(function ($relation) use ($key) {
-                        return transform([$key, static::resourceIdFromModel($relation)], function ($uniqueKey) use ($relation) {
-                            $this->loadedRelationshipsMap[$relation] = $uniqueKey;
+                    return [$key => ['data' => $relations->map(function ($relation) use ($key, $isUnique) {
+                        return transform([$key, static::resourceIdFromModel($relation)], function ($uniqueKey) use ($relation, $isUnique) {
+                            $this->loadedRelationshipsMap[$relation] = [...$uniqueKey, $isUnique];
 
                             return ['id' => $uniqueKey[1], 'type' => $uniqueKey[0]];
                         });
                     })]];
                 }
 
-                return [$key => ['data' => transform(
+                if (is_null($relations) || $relations instanceof Pivot || in_array(AsPivot::class, class_uses_recursive($relations), true)) {
+                    return [$key => null];
+                }
+
+                return [$key => ['data' => [transform(
                     [static::resourceTypeFromModel($relations), static::resourceIdFromModel($relations)],
                     function ($uniqueKey) use ($relations) {
-                        $this->loadedRelationshipsMap[$relations] = $uniqueKey;
+                        $this->loadedRelationshipsMap[$relations] = [...$uniqueKey, true];
 
                         return ['id' => $uniqueKey[1], 'type' => $uniqueKey[0]];
                     }
-                )]];
-            })->all();
+                )]]];
+            })->filter()->all();
     }
 
     /**
      * Resolves `included` for the resource.
      */
     public function resolveIncludedResources(Request $request): array
     {
+        if (! $this->resource instanceof Model) {
+            return [];
+        }
+
         $this->compileResourceRelationships($request);
 
         $relations = new Collection;
 
-        foreach ($this->loadedRelationshipsMap as $relation => $uniqueKey) {
+        foreach ($this->loadedRelationshipsMap as $relation => $value) {
             $resourceInstance = rescue(fn () => $relation->toResource(), new JsonApiResource($relation), false);
 
             if (! $resourceInstance instanceof JsonApiResource &&
                 $resourceInstance instanceof JsonResource) {
                 $resourceInstance = new JsonApiResource($resourceInstance->resource);
             }
 
+            [$type, $id, $isUnique] = $value;
+
             $relations->push([
-                'id' => $uniqueKey[1],
-                'type' => $uniqueKey[0],
+                'id' => $id,
+                'type' => $type,
+                '_uniqueKey' => $isUnique === true ? [$id, $type] : [$id, $type, (string) Str::random()],
                 'attributes' => Arr::get($resourceInstance->resolve($request), 'data.attributes', []),
             ]);
         }
 
-        return $relations->uniqueStrict(
-            fn ($relation): array => [$relation['id'], $relation['type']]
-        )->all();
+        return $relations->uniqueStrict(fn ($relation): array => $relation['_uniqueKey'])
+            ->map(fn ($relation): array => Arr::except($relation, ['_uniqueKey']))
+            ->all();
     }
 
     /**

src/Illuminate/Http/Resources/JsonApi/JsonApiResource.php

@@ -51,6 +51,15 @@ public static function configure(?string $version = null, array $ext = [], array
         ]);
     }
 
+    public function toRelationships(Request $request)
+    {
+        if (property_exists($this, 'relationships')) {
+            return $this->relationships;
+        }
+
+        return [];
+    }
+
     /**
      * Get the resource's ID.
      *