title: Uncaught BadMethodCallException: Object->__call(): the method 'Slides' does not exist on 'Page'
body: <p>I'm having trouble finding a solution for this. Here is my code:</p>
  
  <pre><code>class Page extends SiteTree
  {
      private static $many_many = [
          'Slides' =&gt; SliderImage::class,
      ];
  
      private static $many_many_extraFields = [
          'Slides' =&gt; ['SlideSort' =&gt; 'Int'],
      ];
  
      private static $table_name = 'Page';
  
      public function getCMSFields() {
          $fields = parent::getCMSFields();
          $fields-&gt;addFieldToTab(
              'Root.Gallery',
              $grid = GridField::create(
                  'Slides',
                  'Slides',
                  $this-&gt;Slides(),
                  GridFieldConfig_RelationEditor::create()
                      -&gt;addComponent(GridFieldOrderableRows::create('SlideSort'))
              )
          );
          return $fields;
      }
  
  }
  </code></pre>
  
  <p>I get this error: <code>[Emergency] Uncaught BadMethodCallException: Object-&gt;__call(): the method 'Slides' does not exist on 'Page'</code></p>