CheckListTree::attach

static function attach($id, $parentId = 0, array $parameters = [])
{
	$result = static::canAttach($id, $parentId);

	$replaces = [
		'#ID#' => $id,
		'#PARENT_ID#' => $parentId,
	];

	if ($result->isSuccess())
	{
		// check if link is already exists
		if ($parentId && static::isPathExist($parentId, $id, ['DIRECT' => true]))
		{
			$result = static::addErrorToResult($result, $replaces, __METHOD__, 'PATH_EXISTS');
			return $result;
		}

		if (static::isNodeExist($id))
		{
			if ($parameters['NEW_NODE'] ?? null)
			{
				$result = static::addErrorToResult($result, $replaces, __METHOD__, 'EXISTING_NODE_ADDING');
			}
			else
			{
				// we should do detach node from the previous point, if any
				$detachResult = static::detach($id);
				$result->loadErrors($detachResult->getErrors());
			}
		}

		// if !$parentId, then it behaves like detach()
		if ($parentId && $result->isSuccess())
		{
			$connection = Application::getConnection();

			$tableName = static::getTableName();
			$parentColumnName = static::getParentNodeColumnName();
			$childColumnName = static::getNodeColumnName();
			$levelColumnName = static::getLevelColumnName();

			// attach to a new point
			static::ensureNodeExists($parentId);
			static::ensureNodeExists($id);

			// now link each item of path to $parentId with each item of subtree of $id
			$connection->query("
				INSERT INTO {$tableName} (PARENT_ID, CHILD_ID, LEVEL)
				SELECT P.{$parentColumnName},
					   CH.{$childColumnName},
					   P.{$levelColumnName} + CH.{$levelColumnName} + 1 AS {$levelColumnName}
				FROM {$tableName} P
				CROSS JOIN (
					SELECT {$id} AS {$childColumnName}, 0 AS {$levelColumnName}
					UNION
					SELECT CH1.{$childColumnName}, CH2.{$levelColumnName} + 1 AS {$levelColumnName}
					FROM {$tableName} CH1
					LEFT JOIN {$tableName} CH2 ON CH1.{$parentColumnName} = CH2.{$childColumnName}
					WHERE CH2.{$parentColumnName} = {$id} AND CH1.{$levelColumnName} = 1
					) CH
				WHERE P.{$childColumnName} = {$parentId}
			");
		}
	}

	return $result;
}