protected function getData(array $context)
    {
        $data = [];
        switch ($context['action']) {
            case 'UPDATE':
                $diff = $this->diff($context['old'], $context['new']);
                foreach ($diff as $item) {
                    list($k, $old, $new) = $item;
                    if (isset($context['new'][$k])) {
                        $data[$k] = [$old, $new];
                    }
                }
                break;
            case 'INSERT':
                foreach ($context['new'] as $k => $val) {
                    $data[$k] = [null, $val];
                }
                break;
            case 'DELETE':
                foreach ($context['old'] as $k => $val) {
                    $data[$k] = [$val, null];
                }
                break;
        }

        return $data;
    }