OctoberCMS：如何扩展System \ Models \ File并为其添加新字段？

I need to add an extra column to the system_files table. I'd prefer not to change this table, so I decided to add a new table with one column and then extend the System\Models\File model with a hasOne relationship. I therefore created a new table called myname_plugin_tag with two fields: file_id and title and created a new model file for it called Tag:

class Tag extends Model
{
    use \October\Rain\Database\Traits\Validation;

    /*
     * Validation
     */
    public $rules = [
    ];

    /*
     * Disable timestamps by default.
     * Remove this line if timestamps are defined in the database table.
     */
    public $timestamps = false;

    /**
     * @var string The database table used by the model.
     */
    public $table = 'myname_plugin_tag';
}

And in the boot method of my plugin I have:

System\Models\File::extend(function($model){
    $model->hasOne['tag']=[
        'MyName\Plugin\Models\Tag',
        'key' => 'file_id',
        'timestamps' => 'false'
    ];
});

That seems to be all I have to do. But when saving a file with the new relationship I've defined, I get an error.

$user = Auth::getUser();

$tag = new Tag;
$tag->title = 'some tag';

$file = new File;
$file->data = Input::file('catalog');
$file->title = Input::get('title');
$file->tag = $tag; // => This line is the culprit. If I comment it, the exception will not raise

$user->files = $file;
$user->save();

Exception:

Call to undefined method October\Rain\Database\QueryBuilder::withTimestamps() E:\Development\git\catalog-manager\vendor\laravel\framework\src\Illuminate\Database\Query\Builder.php line 2123

If I remove the line 'timestamps' => 'false', the exception gets fixed and $file model will be saved, but $tag model is not saved yet.

Using $file->tag()->save($tag) works and saves the tag! But the problem is not solved. I cannot access the saved property via $user->files[0]->tag and get this error:

Trying to get property of non-object

The output of {{dump($user->files[0])}} clearly shows that tag property has not been added to the File model:

id  integer
disk_name  string
file_name  string
file_size  integer
content_type  string
title  string
description  NULL
field  string
sort_order  integer
created_at  string
updated_at  string
path  string
extension  string

So it seems that the File model is not aware of the new tag property added to it. Is there anything I'm missing?