public function updateAssignments()
    {
        if (!$this->validate()) {
            return false;
        }

        if (!is_array($this->items)) {
            $this->items = [];
        }

        $assignedItems = $this->manager->getItemsByUser($this->user_id);
        $assignedItemsNames = array_keys($assignedItems);

        foreach (array_diff($assignedItemsNames, $this->items) as $item) {
            $this->manager->revoke($assignedItems[$item], $this->user_id);
        }

        foreach (array_diff($this->items, $assignedItemsNames) as $item) {
            $this->manager->assign($this->manager->getItem($item), $this->user_id);
        }

        $this->updated = true;

        return true;
    }