AllowedFields interaction with Laravel API Resources

[vincent-lu]

Hi I'm trying to figure out what my problem is in getting allowedFields to play nice with Laravel API Resources JsonResource::whenLoaded.

The basic setup is something like this:

In my App\Http\Controllers\ProductsController:

public function index(Request $request): LengthAwarePaginator
{
    $products = QueryBuilder::for(Product::class)
        ->allowedFields(['id', 'sku', 'stock.qty'])
        ->allowedIncludes('stock')
        ->get();

    return (ProductResource::collection($products))
        ->paginate(request('limit', 10));
}

In my App\Models\Product:

public function stock(): hasOne
{
    return $this->hasOne(ProductStock::class);
}

For my App\Http\Resources\ProductResource:

public function toArray($request): array
{
    return array_merge(
        $this->resource->toArray(),
        [
            'stock' => new ProductStockResource($this->whenLoaded('stock')),
        ]
    );
}

App\Http\Resources\ProductStockResource:

public function toArray($request): array
{
    return [
        'id' => $this->id,
        'qty' => $this->qty,
    ];
}

When I send the request to ProductsController::index() with ?include=stock&fields[products]=sku&fields[stock]=qty I'm expacting to get something like:

[
    {
        "sku": "TESTSKU",
        "stock": {
            "qty": 5
        }
    }
]

But stead I get:

[
    {
        "sku": "TESTSKU",
        "stock": null
    }
]

It seems when any fields[] parameter is supplied, the $this->whenLoaded('stock') in App\Http\Resources\ProductResource returns null; but If I request ?include=stock only (i.e. without triggering allowedFields), $this->whenLoaded('stock') returns App\Models\ProductStock as expected.

Let me know if anyone knows why fields[] parameter would make Laravel API Resources think the relationship isn't loaded?