How to get all sections of an infoblock, with subsections of all levels of nesting?

Question

1C-Bitrix

Actually the whole point of the question is stated in the title of the question.
Tried using section.list but it only gives sections without subsections.
I would like to do without additional. requests via getlist.

Answer 1

You can specify the desired sampling depth in the component.
Or write your own component
https://dev.1c-bitrix.ru/api_help/iblock/classes/c...
The examples have a selection of subsections

Answer 2

I re-read and did not understand the question at all. There is also a standard CIblockSection::GetList() which for 1 request perfectly gets everything with nesting.
In the spoiler, I indicated the code that will get all sections, including subsections for a specific infoblock, sorted by the left indent (ie, top to bottom, left to right). And all this for 1 request to the database using the API.

An example that I tested

/**
 * Всегда считаем что модуль установлен, 
 * поэтому просто подключаем его
 */
\Bitrix\Main\Loader::IncludeModule('iblock');

/**
 * У меня для тестирования инфоблок с номером 5,
 * у тебя может быть любой другой инфобло
 * 
 * @var array Параметры фильтрации
 */
$arFilter = [
  'IBLOCK_ID' => 5
];

/**
 * В Битриксе разделы хранятся по принципу Nested sets
 * 
 * @var array Параметры сортировки
 */
$arOrder = [
  'LEFT_MARGIN' => 'ASC'
];

/**
 * @var array Поля разделов
 */
$arSelect = [
  'ID',
  'LEFT_MARGIN',
  'DEPTH_LEVEL',
  'NAME'
];

$resSections = \CIBlockSection::GetList($arOrder, $arFilter, false, $arSelect);

while( $arSection = $resSections->fetch() )
{
  var_dump($arSection);
}

What did I do wrong and where am I doing wrong?