class BannerPage extends Page {

    public static $db = array(

    );

    public static $has_one = array(
        "LeftBanner" => "TextBanner",
        "RightBanner" => "TextBanner"
    );

    public function getCMSFields() {
        $fields = parent::getCMSFields();
        $fields->addFieldsToTab("Root.LeftBanner", $this->LeftBanner()->getCMSFields());
        $fields->addFieldsToTab("Root.RightBanner", $this->RightBanner()->getCMSFields());
        return $fields;
    }

}

class BannerPage_Controller extends Page_Controller {

}

class TextBanner extends DataObject {

    public static $db = array(
        "BackgroundColour" => "Varchar(6)",
        "Content" => "HTMLText"
    );

    public static $has_one = array(
        "BottomImage" => "Image"
    );

    public function getCMSFields() {
        return new FieldList(
            new TextField("BackgroundColour", "Background Colour (hex)"),
            new UploadField("BottomImage", "Bottom Image"),
            new HTMLEditorField("Content", "Content")
        );
    }

}