title: Octobercms onSave update other model
body: <p>I need to update the <code>status</code> field of the book in model relation when a loan is saved, but it is not working.</p>
  
  <p>My code</p>
  
  <pre><code>class Lending extends Model
  {
  
  /**
   * @var string The database table used by the model.
   */
  public $table = 'ribsousa_library_lendings';
  
  /*
   * Relations
   */
  public $belongsToMany = [
      'books' =&gt; [
          'Ribsousa\Library\Models\Book',
          'table' =&gt;  'ribsousa_library_lendings_books',
          'order'      =&gt; 'title desc'
      ]
  ];
  
  public function afterSave()
  {
  
      $this-&gt;book-&gt;status = 1;
      $this-&gt;book-&gt;save();
  
  }
  }
  </code></pre>
  
  <p>The Error:</p>
  
  <pre><code>`"Indirect modification of overloaded property Ribsousa\Library\Models\Lending::$book has no effect" on line 95 of C:\wamp64\www\iepm.dev\plugins\ribsousa\library\models\Lending.php`
  </code></pre>