class ArticlePhoto extends DataObject
{
   public static $singular_name = 'Obrázok k článku';
   
   public static $db = array (
      'Title' => 'text'
   );
   
   public static $has_one = array (
      'Image' => 'Image',
      'Page' => 'Page',
      );
}

class Article extends Page
{

   public static $has_many = array(
      'ArticlePhotos' => 'ArticlePhoto'
   );
   
   public function getCMSFields()
   {
      $f = parent::getCMSFields();
      
      $dl = DataList::create('ArticlePhoto')
         ->where('PageID ='.$this->ID);
      
      $config = new GridFieldConfig_RelationEditor();
            
      $gridField = new GridField('ArticlePhotos','ArticlePhotoGallert', $dl,$config);
            
      $f -> addFieldToTab('Root.PhotoGallery', $gridField);
      return $f;
   }
}