File.php

<?php

namespace CFS;
use Eloquent;

class File extends Eloquent {

    protected $table = 'cfs_files';

    protected $guarded = array('id');

    protected $hidden = array('id');

    protected $touches = array('folder');

    public function folder() {
        return $this->belongsTo('CFS\Folder');
    }

// ...

}

Folder.php

<?php

namespace CFS;
use Eloquent;

class Folder extends Eloquent {

    protected $table = 'cfs_folders';

    protected $guarded = array('id');

    public function files() {
        return $this->hasMany('CFS\File', 'folder_id');
    }

// ...

}