View file upload/library/XenForo/DataWriter/Helper/User.php

<?php

class XenForo_DataWriter_Helper_User
{
	public static function verifyUserId(&$user_id, XenForo_DataWriter $dw, $fieldName = false)
	{
		$db = XenForo_Application::getDb();
		$existing_user_id = $db->fetchOne('
				SELECT user_id
				FROM xf_user
				WHERE user_id = ?
			', $user_id);

		if ($existing_user_id == $user_id)
		{
			return true;
		}

		$dw->error(new XenForo_Phrase('requested_user_not_found'), $fieldName);
		return false;
	}

	public static function updateSecondaryUserGroupIds($userId, $newGroupIds, $oldGroupIds)
	{
		$userDw = XenForo_DataWriter::create('XenForo_DataWriter_User');
		$userDw->setExistingData($userId);
		if ($userDw->get('secondary_group_ids'))
		{
			$existingGroups = array_fill_keys(explode(',', $userDw->get('secondary_group_ids')), true);
		}
		else
		{
			$existingGroups = array();
		}

		if ($oldGroupIds)
		{
			foreach(explode(',', $oldGroupIds) AS $groupId)
			{
				unset($existingGroups[$groupId]);
			}
		}

		if ($newGroupIds)
		{
			foreach(explode(',', $newGroupIds) AS $groupId)
			{
				$existingGroups[$groupId] = true;
			}
		}

		$userDw->setSecondaryGroups(array_keys($existingGroups));
		$userDw->save();

		return $userDw;
	}

	/**
	 * Verifies the extra user group IDs.
	 *
	 * @param array|string $userGroupIds Array or comma-delimited list
	 *
	 * @return boolean
	 */
	public static function verifyExtraUserGroupIds(&$userGroupIds, XenForo_DataWriter $dw, $fieldName = false)
	{
		if (!is_array($userGroupIds))
		{
			if ($userGroupIds === '')
			{
				return true;
			}
			$userGroupIds = preg_split('#,\s*#', $userGroupIds);
		}

		if (!$userGroupIds)
		{
			$userGroupIds = '';
			return true;
		}

		$userGroupIds = array_map('intval', $userGroupIds);
		$userGroupIds = array_unique($userGroupIds);
		sort($userGroupIds, SORT_NUMERIC);
		$userGroupIds = implode(',', $userGroupIds);

		return true;
	}
}