diff --git a/src/Illuminate/Http/Resources/Json/JsonResource.php b/src/Illuminate/Http/Resources/Json/JsonResource.php
index 02ebce156d8c..7590a95d8eb0 100644
--- a/src/Illuminate/Http/Resources/Json/JsonResource.php
+++ b/src/Illuminate/Http/Resources/Json/JsonResource.php
@@ -111,7 +111,7 @@ protected static function newCollection($resource)
      */
     public function resolve($request = null)
     {
-        $data = $this->toAttributes(
+        $data = $this->resolveResourceData(
             $request ?: $this->resolveRequestFromContainer()
         );
 
@@ -132,9 +132,24 @@ public function resolve($request = null)
      */
     public function toAttributes(Request $request)
     {
+        if (property_exists($this, 'attributes')) {
+            return $this->attributes;
+        }
+
         return $this->toArray($request);
     }
 
+    /**
+     * Resolve the resource data to an array.
+     *
+     * @param  \Illuminate\Http\Request  $request
+     * @return array
+     */
+    public function resolveResourceData(Request $request)
+    {
+        return $this->toAttributes($request);
+    }
+
     /**
      * Transform the resource into an array.
      *
diff --git a/src/Illuminate/Http/Resources/JsonApi/Concerns/ResolvesJsonApiElements.php b/src/Illuminate/Http/Resources/JsonApi/Concerns/ResolvesJsonApiElements.php
index 2b2a4ef4e5da..1ea9188f7792 100644
--- a/src/Illuminate/Http/Resources/JsonApi/Concerns/ResolvesJsonApiElements.php
+++ b/src/Illuminate/Http/Resources/JsonApi/Concerns/ResolvesJsonApiElements.php
@@ -2,6 +2,7 @@
 
 namespace Illuminate\Http\Resources\JsonApi\Concerns;
 
+use Generator;
 use Illuminate\Contracts\Support\Arrayable;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\AsPivot;
@@ -12,21 +13,32 @@
 use Illuminate\Http\Resources\JsonApi\Exceptions\ResourceIdentificationException;
 use Illuminate\Http\Resources\JsonApi\JsonApiRequest;
 use Illuminate\Http\Resources\JsonApi\JsonApiResource;
+use Illuminate\Http\Resources\JsonApi\RelationResolver;
 use Illuminate\Http\Resources\MissingValue;
 use Illuminate\Support\Arr;
 use Illuminate\Support\Collection;
+use Illuminate\Support\LazyCollection;
 use Illuminate\Support\Str;
 use JsonSerializable;
-use WeakMap;
 
 trait ResolvesJsonApiElements
 {
+    /**
+     * Determine whether resources respect inclusions and fields from the request.
+     */
+    protected bool $usesRequestQueryString = true;
+
+    /**
+     * Determine whether included relationship for the resource from eager loaded relationship.
+     */
+    protected bool $includesPreviouslyLoadedRelationships = false;
+
     /**
      * Cached loaded relationships map.
      *
-     * @var \WeakMap|null
+     * @var array<int, array{0: \Illuminate\Http\Resources\JsonApi\JsonApiResource, 1: string, 2: string, 3: bool}|null
      */
-    protected $loadedRelationshipsMap;
+    public $loadedRelationshipsMap;
 
     /**
      * Cached loaded relationships identifers.
@@ -36,7 +48,7 @@ trait ResolvesJsonApiElements
     /**
      * Resolves `data` for the resource.
      */
-    public function resolveResourceData(JsonApiRequest $request): array
+    protected function resolveResourceObject(JsonApiRequest $request): array
     {
         $resourceType = $this->resolveResourceType($request);
 
@@ -59,7 +71,7 @@ public function resolveResourceData(JsonApiRequest $request): array
      *
      * @throws ResourceIdentificationException
      */
-    protected function resolveResourceIdentifier(JsonApiRequest $request): string
+    public function resolveResourceIdentifier(JsonApiRequest $request): string
     {
         if (! is_null($resourceId = $this->toId($request))) {
             return $resourceId;
@@ -78,7 +90,7 @@ protected function resolveResourceIdentifier(JsonApiRequest $request): string
      *
      * @throws ResourceIdentificationException
      */
-    protected function resolveResourceType(JsonApiRequest $request): string
+    public function resolveResourceType(JsonApiRequest $request): string
     {
         if (! is_null($resourceType = $this->toType($request))) {
             return $resourceType;
@@ -107,11 +119,15 @@ protected function resolveResourceAttributes(JsonApiRequest $request, string $re
             $data = $data->jsonSerialize();
         }
 
-        $sparseFieldset = $request->sparseFields($resourceType);
+        $sparseFieldset = match ($this->usesRequestQueryString) {
+            true => $request->sparseFields($resourceType),
+            default => [],
+        };
 
         $data = (new Collection($data))
             ->mapWithKeys(fn ($value, $key) => is_int($key) ? [$value => $this->resource->{$value}] : [$key => $value])
             ->when(! empty($sparseFieldset), fn ($attributes) => $attributes->only($sparseFieldset))
+            ->reject(fn ($value, $key) => $key === $this->resource->getKey())
             ->transform(fn ($value) => value($value, $request))
             ->all();
 
@@ -136,7 +152,7 @@ protected function resolveResourceRelationshipIdentifiers(JsonApiRequest $reques
         return [
             ...(new Collection($this->filter($this->loadedRelationshipIdentifiers)))
                 ->map(function ($relation) {
-                    return ! is_null($relation) ? $relation : ['data' => []];
+                    return ! is_null($relation) ? $relation : ['data' => null];
                 })->all(),
         ];
     }
@@ -146,67 +162,135 @@ protected function resolveResourceRelationshipIdentifiers(JsonApiRequest $reques
      */
     protected function compileResourceRelationships(JsonApiRequest $request): void
     {
-        if ($this->loadedRelationshipsMap instanceof WeakMap) {
+        if (! is_null($this->loadedRelationshipsMap)) {
             return;
         }
 
-        $sparseIncluded = $request->sparseIncluded();
+        $sparseIncluded = match (true) {
+            $this->includesPreviouslyLoadedRelationships => array_keys($this->resource->getRelations()),
+            default => $request->sparseIncluded(),
+        };
 
         $resourceRelationships = (new Collection($this->toRelationships($request)))
-            ->mapWithKeys(fn ($value, $key) => is_int($key) ? [$value => fn () => $this->resource->{$value}] : [$key => $value])
+            ->transform(fn ($value, $key) => is_int($key) ? new RelationResolver($value) : new RelationResolver($key, $value))
+            ->mapWithKeys(fn ($relationResolver) => [$relationResolver->relationName => $relationResolver])
             ->filter(fn ($value, $key) => in_array($key, $sparseIncluded));
 
         $resourceRelationshipKeys = $resourceRelationships->keys();
 
-        $this->resource->loadMissing($resourceRelationshipKeys->all());
+        $this->resource->loadMissing($resourceRelationshipKeys->all() ?? []);
 
-        $this->loadedRelationshipsMap = new WeakMap;
+        $this->loadedRelationshipsMap = [];
 
-        $this->loadedRelationshipIdentifiers = $resourceRelationships->mapWithKeys(function ($relationResolver, $key) {
-            $relatedModels = value($relationResolver);
+        $this->loadedRelationshipIdentifiers = (new LazyCollection(function () use ($request, $resourceRelationships) {
+            foreach ($resourceRelationships as $relationName => $relationResolver) {
+                $relatedModels = $relationResolver->handle($this->resource);
+                $relatedResourceClass = $relationResolver->resourceClass();
 
-            // Relationship is a collection of models...
-            if ($relatedModels instanceof Collection) {
-                $relatedModels = $relatedModels->values();
-
-                if ($relatedModels->isEmpty()) {
-                    return [$key => ['data' => $relatedModels]];
+                if (! is_null($relatedModels)) {
+                    $relatedModels->loadMissing($request->sparseIncluded($relationName));
                 }
 
-                $relationship = $this->resource->{$key}();
+                yield from $this->compileResourceRelationshipUsingResolver(
+                    $request,
+                    $this->resource,
+                    $relationResolver,
+                    $relatedModels,
+                );
+            }
+        }))->all();
+    }
 
-                $isUnique = ! $relationship instanceof BelongsToMany;
+    /**
+     * Compile resource relations.
+     */
+    protected function compileResourceRelationshipUsingResolver(
+        JsonApiRequest $request,
+        mixed $resource,
+        RelationResolver $relationResolver,
+        Collection|Model|null $relatedModels
+    ): Generator {
+        $relationName = $relationResolver->relationName;
+        $resourceClass = $relationResolver->resourceClass();
+
+        // Relationship is a collection of models...
+        if ($relatedModels instanceof Collection) {
+            $relatedModels = $relatedModels->values();
+
+            if ($relatedModels->isEmpty()) {
+                yield $relationName => ['data' => $relatedModels];
+
+                return;
+            }
 
-                $key = static::resourceTypeFromModel($relatedModels->first());
+            $relationship = $resource->{$relationName}();
 
-                return [$key => ['data' => $relatedModels->map(function ($relation) use ($key, $isUnique) {
-                    return transform([$key, static::resourceIdFromModel($relation)], function ($uniqueKey) use ($relation, $isUnique) {
-                        $this->loadedRelationshipsMap[$relation] = [...$uniqueKey, $isUnique];
+            $isUnique = ! $relationship instanceof BelongsToMany;
 
-                        return ['id' => $uniqueKey[1], 'type' => $uniqueKey[0]];
-                    });
-                })]];
-            }
+            yield $relationName => ['data' => $relatedModels->map(function ($relatedModel) use ($request, $resourceClass, $isUnique) {
+                $relatedResource = rescue(fn () => $relatedModel->toResource($resourceClass), new JsonApiResource($relatedModel));
 
-            // Relationship is a single model...
-            $relatedModel = $relatedModels;
+                return transform(
+                    [$relatedResource->resolveResourceType($request), $relatedResource->resolveResourceIdentifier($request)],
+                    function ($uniqueKey) use ($request, $relatedModel, $relatedResource, $isUnique) {
+                        $this->loadedRelationshipsMap[] = [$relatedResource, ...$uniqueKey, $isUnique];
 
-            if (is_null($relatedModel)) {
-                return [$key => null];
-            } elseif ($relatedModel instanceof Pivot ||
-                in_array(AsPivot::class, class_uses_recursive($relatedModel), true)) {
-                return [$key => new MissingValue];
-            }
+                        $this->compileIncludedNestedRelationshipsMap($request, $relatedModel, $relatedResource);
 
-            return [$key => ['data' => [transform(
-                [static::resourceTypeFromModel($relatedModel), static::resourceIdFromModel($relatedModel)],
-                function ($uniqueKey) use ($relatedModel) {
-                    $this->loadedRelationshipsMap[$relatedModel] = [...$uniqueKey, true];
+                        return [
+                            'id' => $uniqueKey[1],
+                            'type' => $uniqueKey[0],
+                        ];
+                    }
+                );
+            })->all()];
 
-                    return ['id' => $uniqueKey[1], 'type' => $uniqueKey[0]];
-                }
-            )]]];
-        })->all();
+            return;
+        }
+
+        // Relationship is a single model...
+        $relatedModel = $relatedModels;
+
+        if (is_null($relatedModel)) {
+            yield $relationName => null;
+
+            return;
+        } elseif ($relatedModel instanceof Pivot ||
+            in_array(AsPivot::class, class_uses_recursive($relatedModel), true)) {
+            yield $relationName => new MissingValue;
+
+            return;
+        }
+
+        $relatedResource = rescue(fn () => $relatedModel->toResource($resourceClass), new JsonApiResource($relatedModel));
+
+        yield $relationName => ['data' => transform(
+            [$relatedResource->resolveResourceType($request), $relatedResource->resolveResourceIdentifier($request)],
+            function ($uniqueKey) use ($relatedModel, $relatedResource, $request) {
+                $this->loadedRelationshipsMap[] = [$relatedResource, ...$uniqueKey, true];
+
+                $this->compileIncludedNestedRelationshipsMap($request, $relatedModel, $relatedResource);
+
+                return [
+                    'id' => $uniqueKey[1],
+                    'type' => $uniqueKey[0],
+                ];
+            }
+        )];
+    }
+
+    /**
+     * Compile included relationships map.
+     */
+    protected function compileIncludedNestedRelationshipsMap(JsonApiRequest $request, Model $relation, JsonApiResource $resource): void
+    {
+        (new Collection($resource->toRelationships($request)))
+            ->transform(fn ($value, $key) => is_int($key) ? new RelationResolver($value) : new RelationResolver($key, $value))
+            ->mapWithKeys(fn ($relationResolver) => [$relationResolver->relationName => $relationResolver])
+            ->filter(fn ($value, $key) => in_array($key, array_keys($relation->getRelations())))
+            ->each(function ($relationResolver, $key) use ($relation, $request) {
+                $this->compileResourceRelationshipUsingResolver($request, $relation, $relationResolver, $relation->getRelation($key));
+            });
     }
 
     /**
@@ -222,22 +306,34 @@ public function resolveIncludedResources(JsonApiRequest $request): array
 
         $relations = new Collection;
 
-        foreach ($this->loadedRelationshipsMap as $relation => $value) {
-            $resourceInstance = rescue(fn () => $relation->toResource(), new JsonApiResource($relation), false);
+        $index = 0;
+
+        while ($index < count($this->loadedRelationshipsMap)) {
+            [$resourceInstance, $type, $id, $isUnique] = $this->loadedRelationshipsMap[$index];
 
             if (! $resourceInstance instanceof JsonApiResource &&
                 $resourceInstance instanceof JsonResource) {
                 $resourceInstance = new JsonApiResource($resourceInstance->resource);
             }
 
-            [$type, $id, $isUnique] = $value;
+            $relationsData = $resourceInstance
+                ->withoutRequestQueryString()
+                ->includePreviouslyLoadedRelationships()
+                ->resolve($request);
 
-            $relations->push([
+            array_push($this->loadedRelationshipsMap, ...$resourceInstance->loadedRelationshipsMap);
+
+            $relations->push(array_filter([
                 'id' => $id,
                 'type' => $type,
                 '_uniqueKey' => $isUnique === true ? [$id, $type] : [$id, $type, (string) Str::random()],
-                'attributes' => Arr::get($resourceInstance->resolve($request), 'data.attributes', []),
-            ]);
+                'attributes' => Arr::get($relationsData, 'data.attributes'),
+                'relationships' => Arr::get($relationsData, 'data.relationships'),
+                'links' => Arr::get($relationsData, 'data.links'),
+                'meta' => Arr::get($relationsData, 'data.meta'),
+            ]));
+
+            $index++;
         }
 
         return $relations->uniqueStrict(fn ($relation) => $relation['_uniqueKey'])
@@ -268,7 +364,7 @@ protected function resolveResourceMetaInformation(JsonApiRequest $request): arra
     /**
      * Get the resource ID from the given Eloquent model.
      */
-    protected static function resourceIdFromModel(Model $model): string
+    public static function resourceIdFromModel(Model $model): string
     {
         return $model->getKey();
     }
@@ -276,14 +372,56 @@ protected static function resourceIdFromModel(Model $model): string
     /**
      * Get the resource type from the given Eloquent model.
      */
-    protected static function resourceTypeFromModel(Model $model): string
+    public static function resourceTypeFromModel(Model $model): string
     {
         $modelClassName = $model::class;
 
         $morphMap = Relation::getMorphAlias($modelClassName);
 
-        return Str::of(
+        return static::normalizeResourceType(
             $morphMap !== $modelClassName ? $morphMap : class_basename($modelClassName)
-        )->snake()->pluralStudly();
+        );
+    }
+
+    /**
+     * Indicate that relationship loading should respect the request's "includes" query string.
+     *
+     * @return $this
+     */
+    public function withRequestQueryString(bool $value = true)
+    {
+        $this->usesRequestQueryString = $value;
+
+        return $this;
+    }
+
+    /**
+     * Indicate that relationship loading should not rely on the request's "includes" query string.
+     *
+     * @return $this
+     */
+    public function withoutRequestQueryString()
+    {
+        return $this->withRequestQueryString(false);
+    }
+
+    /**
+     * Determine relationship should include loaded relationships.
+     *
+     * @return $this
+     */
+    public function includePreviouslyLoadedRelationships()
+    {
+        $this->includesPreviouslyLoadedRelationships = true;
+
+        return $this;
+    }
+
+    /**
+     * Normalize the resource type.
+     */
+    public static function normalizeResourceType(string $value): string
+    {
+        return Str::of($value)->snake()->pluralStudly();
     }
 }
diff --git a/src/Illuminate/Http/Resources/JsonApi/JsonApiRequest.php b/src/Illuminate/Http/Resources/JsonApi/JsonApiRequest.php
index c5f0f194b1bb..c869f1382578 100644
--- a/src/Illuminate/Http/Resources/JsonApi/JsonApiRequest.php
+++ b/src/Illuminate/Http/Resources/JsonApi/JsonApiRequest.php
@@ -3,31 +3,63 @@
 namespace Illuminate\Http\Resources\JsonApi;
 
 use Illuminate\Http\Request;
-use Illuminate\Support\Arr;
+use Illuminate\Support\Collection;
 
 class JsonApiRequest extends Request
 {
+    /**
+     * Cached sparse fieldset.
+     */
+    protected ?array $cachedSparseFields = null;
+
+    /**
+     * Cached sparse included.
+     */
+    protected ?array $cachedSparseIncluded = null;
+
     /**
      * Get the request's included fields.
      */
     public function sparseFields(string $key): array
     {
-        $fieldsets = Arr::get($this->array('fields'), $key, '');
+        if (is_null($this->cachedSparseFields)) {
+            $this->cachedSparseFields = (new Collection($this->array('fields')))
+                ->transform(fn ($fieldsets) => empty($fieldsets) ? [] : explode(',', $fieldsets))
+                ->all();
+        }
 
-        return empty($fieldsets)
-            ? []
-            : explode(',', $fieldsets);
+        return $this->cachedSparseFields[$key] ?? [];
     }
 
     /**
      * Get the request's included relationships.
      */
-    public function sparseIncluded(): array
+    public function sparseIncluded(?string $key = null): ?array
     {
-        $included = (string) $this->string('include', '');
+        if (is_null($this->cachedSparseIncluded)) {
+            $included = (string) $this->string('include', '');
+
+            $this->cachedSparseIncluded = (new Collection(empty($included) ? [] : explode(',', $included)))
+                ->transform(function ($item) {
+                    $with = null;
+
+                    if (str_contains($item, '.')) {
+                        [$relation, $with] = explode('.', $item, 2);
+                    } else {
+                        $relation = $item;
+                    }
+
+                    return ['relation' => $relation, 'with' => $with];
+                })->mapToGroups(fn ($item) => [$item['relation'] => $item['with']])
+                ->toArray();
+        }
+
+        if (is_null($key)) {
+            return array_keys($this->cachedSparseIncluded);
+        }
 
-        return empty($included)
-            ? []
-            : explode(',', $included);
+        return transform($this->cachedSparseIncluded[$key] ?? null, function ($value) {
+            return array_filter($value);
+        }) ?? [];
     }
 }
diff --git a/src/Illuminate/Http/Resources/JsonApi/JsonApiResource.php b/src/Illuminate/Http/Resources/JsonApi/JsonApiResource.php
index 003ffa41a6d1..e764132d197e 100644
--- a/src/Illuminate/Http/Resources/JsonApi/JsonApiResource.php
+++ b/src/Illuminate/Http/Resources/JsonApi/JsonApiResource.php
@@ -153,6 +153,18 @@ public function resolve($request = null)
         ];
     }
 
+    /**
+     * Resolve the resource data to an array.
+     *
+     * @param  \Illuminate\Http\Request  $request
+     * @return array
+     */
+    #[\Override]
+    public function resolveResourceData(Request $request)
+    {
+        return $this->resolveResourceObject($request);
+    }
+
     /**
      * Customize the outgoing response for the resource.
      */
diff --git a/src/Illuminate/Http/Resources/JsonApi/RelationResolver.php b/src/Illuminate/Http/Resources/JsonApi/RelationResolver.php
new file mode 100644
index 000000000000..772acff826a9
--- /dev/null
+++ b/src/Illuminate/Http/Resources/JsonApi/RelationResolver.php
@@ -0,0 +1,62 @@
+<?php
+
+namespace Illuminate\Http\Resources\JsonApi;
+
+use Closure;
+use Illuminate\Database\Eloquent\Collection;
+use Illuminate\Database\Eloquent\Model;
+
+/**
+ * @internal
+ */
+class RelationResolver
+{
+    /**
+     * The relation resolver.
+     *
+     * @var \Closure(mixed):(\Illuminate\Database\Eloquent\Collection|\Illuminate\Database\Eloquent\Model|null)
+     */
+    public Closure $relationResolver;
+
+    /**
+     * The relation resource class.
+     *
+     * @var class-string<\Illuminate\Http\Resources\JsonApi\JsonApiResource>|null
+     */
+    public ?string $relationResourceClass = null;
+
+    /**
+     * Construct a new resource relationship resolver.
+     *
+     * @param  \Closure(mixed):(\Illuminate\Database\Eloquent\Collection|\Illuminate\Database\Eloquent\Model|null)|class-string<\Illuminate\Http\Resources\JsonApi\JsonApiResource>|null  $resolver
+     */
+    public function __construct(public string $relationName, Closure|string|null $resolver = null)
+    {
+        $this->relationResolver = match (true) {
+            $resolver instanceof Closure => $resolver,
+            default => fn ($resource) => $resource->getRelation($this->relationName),
+        };
+
+        if (is_string($resolver) && class_exists($resolver)) {
+            $this->relationResourceClass = $resolver;
+        }
+    }
+
+    /**
+     * Resolve the relation for a resource.
+     */
+    public function handle(mixed $resource): Collection|Model|null
+    {
+        return value($this->relationResolver, $resource);
+    }
+
+    /**
+     * Get the resource class.
+     *
+     * @return class-string<\Illuminate\Http\Resources\JsonApi\JsonApiResource>|null
+     */
+    public function resourceClass(): ?string
+    {
+        return $this->relationResourceClass;
+    }
+}
diff --git a/tests/Integration/Http/Resources/JsonApi/Fixtures/AuthorApiResource.php b/tests/Integration/Http/Resources/JsonApi/Fixtures/AuthorApiResource.php
new file mode 100644
index 000000000000..227723bbc1b2
--- /dev/null
+++ b/tests/Integration/Http/Resources/JsonApi/Fixtures/AuthorApiResource.php
@@ -0,0 +1,29 @@
+<?php
+
+namespace Illuminate\Tests\Integration\Http\Resources\JsonApi\Fixtures;
+
+use Illuminate\Http\Request;
+use Illuminate\Http\Resources\JsonApi\JsonApiResource;
+
+class AuthorApiResource extends JsonApiResource
+{
+    protected array $relationships = [
+        'comments',
+        'profile',
+    ];
+
+    #[\Override]
+    public function toAttributes(Request $request)
+    {
+        return [
+            'name' => $this->name,
+            'email' => $this->email,
+        ];
+    }
+
+    #[\Override]
+    public function toType(Request $request)
+    {
+        return 'authors';
+    }
+}
diff --git a/tests/Integration/Http/Resources/JsonApi/Fixtures/Comment.php b/tests/Integration/Http/Resources/JsonApi/Fixtures/Comment.php
new file mode 100644
index 000000000000..aa9d4926db88
--- /dev/null
+++ b/tests/Integration/Http/Resources/JsonApi/Fixtures/Comment.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace Illuminate\Tests\Integration\Http\Resources\JsonApi\Fixtures;
+
+use Illuminate\Database\Eloquent\Attributes\UseFactory;
+use Illuminate\Database\Eloquent\Attributes\UseResource;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+
+#[UseFactory(CommentFactory::class)]
+#[UseResource(CommentApiResource::class)]
+class Comment extends Model
+{
+    use HasFactory;
+
+    public function post()
+    {
+        return $this->belongsTo(Post::class);
+    }
+
+    public function commenter()
+    {
+        return $this->belongsTo(User::class, 'user_id');
+    }
+}
diff --git a/tests/Integration/Http/Resources/JsonApi/Fixtures/CommentApiResource.php b/tests/Integration/Http/Resources/JsonApi/Fixtures/CommentApiResource.php
new file mode 100644
index 000000000000..d874417ebd30
--- /dev/null
+++ b/tests/Integration/Http/Resources/JsonApi/Fixtures/CommentApiResource.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace Illuminate\Tests\Integration\Http\Resources\JsonApi\Fixtures;
+
+use Illuminate\Http\Resources\JsonApi\JsonApiResource;
+
+class CommentApiResource extends JsonApiResource
+{
+    /**
+     * The resource's attributes.
+     */
+    public $attributes = [
+        'content',
+    ];
+
+    /**
+     * The resource's relationships.
+     */
+    public $relationships = [
+        'posts',
+        'commenter' => UserApiResource::class,
+    ];
+}
diff --git a/tests/Integration/Http/Resources/JsonApi/Fixtures/CommentFactory.php b/tests/Integration/Http/Resources/JsonApi/Fixtures/CommentFactory.php
new file mode 100644
index 000000000000..3d6c26308cf7
--- /dev/null
+++ b/tests/Integration/Http/Resources/JsonApi/Fixtures/CommentFactory.php
@@ -0,0 +1,18 @@
+<?php
+
+namespace Illuminate\Tests\Integration\Http\Resources\JsonApi\Fixtures;
+
+use Illuminate\Database\Eloquent\Factories\Factory;
+use Orchestra\Testbench\Factories\UserFactory;
+
+class CommentFactory extends Factory
+{
+    public function definition(): array
+    {
+        return [
+            'post_id' => PostFactory::new(),
+            'user_id' => UserFactory::new(),
+            'content' => $this->faker->words(10, true),
+        ];
+    }
+}
diff --git a/tests/Integration/Http/Resources/JsonApi/Fixtures/Post.php b/tests/Integration/Http/Resources/JsonApi/Fixtures/Post.php
index 143758e2c966..1c583b9ce9cb 100644
--- a/tests/Integration/Http/Resources/JsonApi/Fixtures/Post.php
+++ b/tests/Integration/Http/Resources/JsonApi/Fixtures/Post.php
@@ -13,8 +13,13 @@ class Post extends Model
 {
     use HasFactory;
 
-    public function user()
+    public function comments()
     {
-        return $this->belongsTo(User::class);
+        return $this->hasMany(Comment::class);
+    }
+
+    public function author()
+    {
+        return $this->belongsTo(User::class, 'user_id');
     }
 }
diff --git a/tests/Integration/Http/Resources/JsonApi/Fixtures/PostApiResource.php b/tests/Integration/Http/Resources/JsonApi/Fixtures/PostApiResource.php
index 6309e6cc5c91..874b703577a3 100644
--- a/tests/Integration/Http/Resources/JsonApi/Fixtures/PostApiResource.php
+++ b/tests/Integration/Http/Resources/JsonApi/Fixtures/PostApiResource.php
@@ -10,4 +10,9 @@ class PostApiResource extends JsonApiResource
         'title',
         'content',
     ];
+
+    protected array $relationships = [
+        'author' => AuthorApiResource::class,
+        'comments',
+    ];
 }
diff --git a/tests/Integration/Http/Resources/JsonApi/Fixtures/User.php b/tests/Integration/Http/Resources/JsonApi/Fixtures/User.php
index ef7cac2097a2..a7adc43ba121 100644
--- a/tests/Integration/Http/Resources/JsonApi/Fixtures/User.php
+++ b/tests/Integration/Http/Resources/JsonApi/Fixtures/User.php
@@ -24,6 +24,11 @@ public function posts()
         return $this->hasMany(Post::class);
     }
 
+    public function comments()
+    {
+        return $this->hasMany(Comment::class);
+    }
+
     public function teams()
     {
         return $this->belongsToMany(Team::class)
diff --git a/tests/Integration/Http/Resources/JsonApi/Fixtures/UserApiResource.php b/tests/Integration/Http/Resources/JsonApi/Fixtures/UserApiResource.php
index 7d1a7c7918c5..6fe76f81db1d 100644
--- a/tests/Integration/Http/Resources/JsonApi/Fixtures/UserApiResource.php
+++ b/tests/Integration/Http/Resources/JsonApi/Fixtures/UserApiResource.php
@@ -8,11 +8,13 @@
 class UserApiResource extends JsonApiResource
 {
     protected array $relationships = [
+        'comments',
         'profile',
         'posts',
         'teams',
     ];
 
+    #[\Override]
     public function toAttributes(Request $request)
     {
         return [
@@ -20,4 +22,10 @@ public function toAttributes(Request $request)
             'email' => $this->email,
         ];
     }
+
+    #[\Override]
+    public function toType(Request $request)
+    {
+        return 'users';
+    }
 }
diff --git a/tests/Integration/Http/Resources/JsonApi/Fixtures/UserResource.php b/tests/Integration/Http/Resources/JsonApi/Fixtures/UserResource.php
index 7ddd2248a37b..05b5e843fccd 100644
--- a/tests/Integration/Http/Resources/JsonApi/Fixtures/UserResource.php
+++ b/tests/Integration/Http/Resources/JsonApi/Fixtures/UserResource.php
@@ -7,6 +7,7 @@
 
 class UserResource extends JsonResource
 {
+    #[\Override]
     public function toArray(Request $request)
     {
         return [
diff --git a/tests/Integration/Http/Resources/JsonApi/Fixtures/migrations.php b/tests/Integration/Http/Resources/JsonApi/Fixtures/migrations.php
index e560a3eb970a..26afadca7cb9 100644
--- a/tests/Integration/Http/Resources/JsonApi/Fixtures/migrations.php
+++ b/tests/Integration/Http/Resources/JsonApi/Fixtures/migrations.php
@@ -34,3 +34,11 @@
 
     $table->index(['team_id', 'user_id']);
 });
+
+Schema::create('comments', function (Blueprint $table) {
+    $table->id();
+    $table->foreignId('post_id')->unique();
+    $table->foreignId('user_id')->index()->nullable();
+    $table->text('content');
+    $table->timestamps();
+});
diff --git a/tests/Integration/Http/Resources/JsonApi/JsonApiCollectionTest.php b/tests/Integration/Http/Resources/JsonApi/JsonApiCollectionTest.php
index b295eddd36cb..0726a1259a0a 100644
--- a/tests/Integration/Http/Resources/JsonApi/JsonApiCollectionTest.php
+++ b/tests/Integration/Http/Resources/JsonApi/JsonApiCollectionTest.php
@@ -107,7 +107,7 @@ public function testItCanGenerateJsonApiResponseWithRelationshipsUsingSparseIncl
                             'email' => $user->email,
                         ],
                         'relationships' => [
-                            'profile' => ['data' => []],
+                            'profile' => ['data' => null],
                             'posts' => ['data' => []],
                             'teams' => ['data' => []],
                         ],
@@ -122,7 +122,8 @@ public function testItCanGenerateJsonApiResponseWithRelationshipsUsingSparseIncl
                         'relationships' => [
                             'profile' => [
                                 'data' => [
-                                    ['id' => (string) $profile->getKey(), 'type' => 'profiles'],
+                                    'id' => (string) $profile->getKey(),
+                                    'type' => 'profiles',
                                 ],
                             ],
                             'posts' => [
diff --git a/tests/Integration/Http/Resources/JsonApi/JsonApiResourceTest.php b/tests/Integration/Http/Resources/JsonApi/JsonApiResourceTest.php
index fe166c5c10ba..82909d11ffdc 100644
--- a/tests/Integration/Http/Resources/JsonApi/JsonApiResourceTest.php
+++ b/tests/Integration/Http/Resources/JsonApi/JsonApiResourceTest.php
@@ -2,6 +2,7 @@
 
 namespace Illuminate\Tests\Integration\Http\Resources\JsonApi;
 
+use Illuminate\Tests\Integration\Http\Resources\JsonApi\Fixtures\Comment;
 use Illuminate\Tests\Integration\Http\Resources\JsonApi\Fixtures\Post;
 use Illuminate\Tests\Integration\Http\Resources\JsonApi\Fixtures\Profile;
 use Illuminate\Tests\Integration\Http\Resources\JsonApi\Fixtures\Team;
@@ -112,7 +113,8 @@ public function testItCanGenerateJsonApiResponseWithRelationshipsUsingSparseIncl
                         ],
                         'profile' => [
                             'data' => [
-                                ['id' => (string) $profile->getKey(), 'type' => 'profiles'],
+                                'id' => (string) $profile->getKey(),
+                                'type' => 'profiles',
                             ],
                         ],
                         'teams' => [
@@ -187,4 +189,140 @@ public function testItCanGenerateJsonApiResponseWithRelationshipsUsingSparseIncl
                 ],
             ]);
     }
+
+    public function test_it_can_resolve_relationship_with_custom_name_and_resource_class()
+    {
+        $now = $this->freezeSecond();
+
+        $user = User::factory()->create();
+
+        $profile = Profile::factory()->create([
+            'user_id' => $user->getKey(),
+            'date_of_birth' => '2011-06-09',
+            'timezone' => 'America/Chicago',
+        ]);
+
+        [$post1, $post2] = Post::factory()->times(2)->create([
+            'user_id' => $user->getKey(),
+        ]);
+
+        $comment = Comment::factory()->create([
+            'post_id' => $post1->getKey(),
+            'user_id' => $user->getKey(),
+        ]);
+
+        $this->getJson("/posts/{$post1->getKey()}?".http_build_query(['include' => 'author']))
+            ->assertHeader('Content-type', 'application/vnd.api+json')
+            ->assertExactJson([
+                'data' => [
+                    'attributes' => [
+                        'content' => $post1->content,
+                        'title' => $post1->title,
+                    ],
+                    'type' => 'posts',
+                    'id' => (string) $post1->getKey(),
+                    'relationships' => [
+                        'author' => [
+                            'data' => [
+                                'id' => (string) $user->getKey(),
+                                'type' => 'authors',
+                            ],
+                        ],
+                    ],
+                ],
+                'included' => [
+                    [
+                        'attributes' => [
+                            'email' => $user->email,
+                            'name' => $user->name,
+                        ],
+                        'id' => (string) $user->getKey(),
+                        'type' => 'authors',
+                    ],
+                ],
+            ])
+            ->assertJsonMissing(['jsonapi']);
+    }
+
+    public function test_it_can_resolve_relationship_with_nested_relationship()
+    {
+        $now = $this->freezeSecond();
+
+        $user = User::factory()->create();
+
+        $profile = Profile::factory()->create([
+            'user_id' => $user->getKey(),
+            'date_of_birth' => '2011-06-09',
+            'timezone' => 'America/Chicago',
+        ]);
+
+        [$post1, $post2] = Post::factory()->times(2)->create([
+            'user_id' => $user->getKey(),
+        ]);
+
+        $comment = Comment::factory()->create([
+            'post_id' => $post1->getKey(),
+            'user_id' => $user->getKey(),
+        ]);
+
+        $this->getJson("/posts/{$post1->getKey()}?".http_build_query(['include' => 'author,comments.commenter']))
+            ->assertHeader('Content-type', 'application/vnd.api+json')
+            ->assertExactJson([
+                'data' => [
+                    'attributes' => [
+                        'content' => $post1->content,
+                        'title' => $post1->title,
+                    ],
+                    'type' => 'posts',
+                    'id' => (string) $post1->getKey(),
+                    'relationships' => [
+                        'author' => [
+                            'data' => [
+                                'id' => (string) $user->getKey(),
+                                'type' => 'authors',
+                            ],
+                        ],
+                        'comments' => [
+                            'data' => [
+                                ['id' => (string) $comment->getKey(), 'type' => 'comments'],
+                            ],
+                        ],
+                    ],
+                ],
+                'included' => [
+                    [
+                        'attributes' => [
+                            'email' => $user->email,
+                            'name' => $user->name,
+                        ],
+                        'id' => (string) $user->getKey(),
+                        'type' => 'authors',
+                    ],
+                    [
+                        'attributes' => [
+                            'content' => $comment->content,
+                        ],
+                        'id' => (string) $comment->getKey(),
+                        'type' => 'comments',
+                        'relationships' => [
+                            'commenter' => [
+                                'data' => [
+                                    'id' => (string) $user->getKey(),
+                                    'type' => 'users',
+                                ],
+                            ],
+                        ],
+                    ],
+                    [
+                        'attributes' => [
+                            'email' => $user->email,
+                            'name' => $user->name,
+                        ],
+                        'id' => (string) $user->getKey(),
+                        'type' => 'users',
+                    ],
+                ],
+            ])
+            ->assertJsonMissing(['jsonapi']);
+    }
 }
diff --git a/tests/Integration/Http/Resources/JsonApi/TestCase.php b/tests/Integration/Http/Resources/JsonApi/TestCase.php
index a1644383a7cb..aa87168d426a 100644
--- a/tests/Integration/Http/Resources/JsonApi/TestCase.php
+++ b/tests/Integration/Http/Resources/JsonApi/TestCase.php
@@ -2,9 +2,11 @@
 
 namespace Illuminate\Tests\Integration\Http\Resources\JsonApi;
 
+use Illuminate\Database\Eloquent\Model;
 use Illuminate\Foundation\Testing\LazilyRefreshDatabase;
 use Illuminate\Http\Resources\Json\JsonResource;
 use Illuminate\Http\Resources\JsonApi\JsonApiResource;
+use Illuminate\Tests\Integration\Http\Resources\JsonApi\Fixtures\Post;
 use Illuminate\Tests\Integration\Http\Resources\JsonApi\Fixtures\User;
 use Orchestra\Testbench\Attributes\WithConfig;
 use Orchestra\Testbench\Attributes\WithMigration;
@@ -15,6 +17,15 @@ abstract class TestCase extends \Orchestra\Testbench\TestCase
 {
     use LazilyRefreshDatabase;
 
+    /** {@inheritdoc} */
+    #[\Override]
+    protected function setUp(): void
+    {
+        Model::shouldBeStrict(true);
+
+        parent::setUp();
+    }
+
     /** {@inheritdoc} */
     #[\Override]
     protected function tearDown(): void
@@ -36,6 +47,14 @@ protected function defineRoutes($router)
         $router->get('users/{userId}', function ($userId) {
             return User::find($userId)->toResource();
         });
+
+        $router->get('posts', function () {
+            return Post::paginate(5)->toResourceCollection();
+        });
+
+        $router->get('posts/{postId}', function ($postId) {
+            return Post::find($postId)->toResource();
+        });
     }
 
     /** {@inheritdoc} */