I'm trying to add an UploadField to to a PageType to store a related File. Obviously doing something stupid, but what :(

use SilverStripe\Assets\File;
use SilverStripe\AssetAdmin\Forms\UploadField;

class FilePage extends Page
{
    private static $has_one = array(
        "FileObject" => "File"
    );

    public function getCMSFields()
    {
        $fields = parent::getCMSFields();

        $fields->addFieldToTab('Root.Main',
            UploadField::create('FileObject', 'My File')
        );
        return $fields;
    }

Generates: Uncaught InvalidArgumentException: has_one relation FilePage.FileObject references class File which doesn't exist.

Same happens with Image. Although both classes exist in the given namespace...

OK - Solved 5 minutes after this post... It works when you:

    private static $has_one = array(
        "FileObject" => "SilverStripe\Assets\File"
    );

or

    private static $has_one = array(
        "FileObject" => File::class
    );

(or also)

    private static $has_one = array(
        "FileObject" => "SilverStripe\\Assets\\File"
    );

use SilverStripe\Assets\File doesn't work, because obviously other classes that handle the relation, don't know about the namespace... Don't know which version is the preferred, as they all are used throughout core...