Custom controller

Standard iblock REST controller \Bitrix\Iblock\Controller\DefaultElement includes the following methods:

Method	Description
getElementEntityAllowedList	Allowed iblock entity fields `\Bitrix\Iblock\ElementTable::getMap`. They are selected by default, when the query doesn't contain `select`.
getAllowedList	List of fields permitted for selection. Default permitted iblock fields from the method `getElementEntityAllowedList` and all iblock properties. If you want to use other fields and specifically, associations, list all the IDs here.
getAction	Retrieves a single element by ID.
listAction	Selects several elements.

Both creating a complete custom and inheriting from standard controller with redefining necessary methods are permitted.

After describing your own custom controller, you must register it in Service Locator Service Locator - is a design pattern for convenient handling of application services.

Find more details in the Bitrix Framework learning course. with the identifier iblock.element.{IBLOCK_API_CODE}.rest.controller, where {IBLOCK_API_CODE} - is API character code value (API_CODE) for your iblock. For example: iblock.element.OfficialNews.rest.controller.

By default, controllers operate only within REST context. Starting from version 20.100.200, public unlimited access to iblock data is available via AJAX-controller mechanism. All prefilters must be cleared:

class MyElement extends \Bitrix\Iblock\Controller\DefaultElement
{
    protected function getDefaultPreFilters()
    {
        return [];
    }
}