问Laravel 3-资源字段错误- BelongsTo -“试图获取非对象的属性'resourceClass‘”

EN

CREATE TABLE `vehicle_service` (
    `id` BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
    `vehicle_id` INT(11) NOT NULL,
)

CREATE TABLE `vehicles` (
    `id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
)

class VehicleService extends Model
{

    protected $table = 'vehicle_service';

    protected $casts = [
        'last_service_date' => 'date',
    ];

    public function vehicle() {
        return $this->belongsTo(Vehicle::class, 'vehicle_id');
    }

}

class VehicleService extends Resource
{

    public static $model = \App\Models\VehicleService::class;

    public function fields(Request $request)
    {
        return [
        ];
    }

    public function fieldsForIndex(NovaRequest $request)
    {
        return [
            BelongsTo::make('Vehicle', 'vehicle', 'App\Nova\Vehicle')
            ->rules('required')
            ->viewable(false),
        ];
    }

    public function fieldsForDetail(NovaRequest $request)
    {
        BelongsTo::make('Vehicle', 'vehicle', 'App\Nova\Vehicle')
        ->viewable(false),
    }
}