public function fluentClasses()
    {
        $classes = [];
        $dataClasses = ClassInfo::subclassesFor(DataObject::class);
        array_shift($dataClasses);
        foreach ($dataClasses as $class) {
            $base = DataObject::getSchema()->baseDataClass($class);
            foreach (DataObject::get_extensions($base) as $extension) {
                if (is_a($extension, FluentExtension::class, true)) {
                    $classes[] = $base;
                    break;
                }
            }
        }
        return array_unique($classes);
    }