Page Class

class Page extends SiteTree {

    private static $db = array(
        'showGallery' => 'Boolean',
        'bgColor' => 'VarChar(7)'
    );

    private static $has_one = array(
        'Background' => 'Image'
    );

     public static $has_many = array(
    'GalleryImages' => 'GalleryImage'
    );


    // Create Grid Field
    public function getCMSFields() {
        $fields = parent::getCMSFields();

        $gridFieldConfig = GridFieldConfig::create()->addComponents(
          new GridFieldToolbarHeader(),
          new GridFieldAddNewButton('toolbar-header-right'),
          new GridFieldSortableHeader(),
          new GridFieldDataColumns(),
          new GridFieldPaginator(10),
          new GridFieldEditButton(),
          new GridFieldDeleteAction(),
          new GridFieldDetailForm()
        );

        $gridField = new GridField("GalleryImages", "Image Gallery", $this->GalleryImages(), $gridFieldConfig);
        $fields->addFieldToTab("Root.Gallery", $gridField);
        $fields->addFieldToTab("Root.Main", new UploadField('Background'));
        $fields->addFieldToTab('Root.Main', new TextField('bgColor', 'Background Color'));
        $fields->addFieldToTab('Root.Main', new CheckboxField('showGallery', 'Auto display gallery'));

        return $fields;
    }

    static $api_access = true;
}

class Page_Controller extends ContentController {

    /**
     * An array of actions that can be accessed via a request. Each array element should be an action name, and the
     * permissions or conditions required to allow the user to access it.
     *
     * <code>
     * array (
     *     'action', // anyone can access this action
     *     'action' => true, // same as above
     *     'action' => 'ADMIN', // you must have ADMIN permissions to access this action
     *     'action' => '->checkAction' // you can only access this action if $this->checkAction() returns true
     * );
     * </code>
     *
     * @var array
     */
    private static $allowed_actions = array ();

    public function init() {
        parent::init();
        // You can include any CSS or JS required by your project here.
        // See: http://doc.silverstripe.org/framework/en/reference/requirements
        // Ejemplo: Requirements::javascript("cms/javascript/LeftAndMain.js");
        // Ejemplo: Requirements::css("cms/css/TreeSelector.css");
    }
}