"wrong number of arguments for 'del' command" when deleting TranslatableModel using Redis cache

[svezina]

Hi all,

Python 3.11 / Django 4.1.4 / django-parler 2.3 / redis 4.4.0

When using the django.core.cache.backends.redis.RedisCache for django cache, deleting a TranslatableModel object will often give the following error:

  File "site-packages\parler\models.py", line 720, in delete
    _delete_cached_translations(self)
  File "site-packages\parler\cache.py", line 181, in _delete_cached_translations
    cache.delete_many(get_object_cache_keys(shared_model))
  File "site-packages\django\core\cache\backends\redis.py", line 229, in delete_many
    self._cache.delete_many(safe_keys)
  File "site-packages\django\core\cache\backends\redis.py", line 152, in delete_many
    client.delete(*keys)
  File "site-packages\redis\commands\core.py", line 1611, in delete
    return self.execute_command("DEL", *names)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "site-packages\redis\client.py", line 1258, in execute_command
    return conn.retry.call_with_retry(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "site-packages\redis\retry.py", line 46, in call_with_retry
    return do()
           ^^^^
  File "site-packages\redis\client.py", line 1259, in <lambda>
    lambda: self._send_command_parse_response(
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "site-packages\redis\client.py", line 1235, in _send_command_parse_response
    return self.parse_response(conn, command_name, **options)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "site-packages\redis\client.py", line 1275, in parse_response
    response = connection.read_response()
               ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "site-packages\redis\connection.py", line 827, in read_response
    raise response
redis.exceptions.ResponseError: wrong number of arguments for 'del' command

It seems to be related to this Django issue which is apparently solved : https://code.djangoproject.com/ticket/33826

The culprit is here in parler/cache.py

def _delete_cached_translations(shared_model):
    cache.delete_many(get_object_cache_keys(shared_model))

When get_object_cache_keys returns an empty list, the error above occurs.

A quick fix would be to simply do

def _delete_cached_translations(shared_model):
    keys = get_object_cache_keys(shared_model)
    if keys:
        cache.delete_many(keys)

This is not a django-parler issue per say, so I haven't sent a pull request. Mind if I do?

Thanks