Added async support (#656)

* Added async logic

* Added tests and fixed async deadlock on aset

* Used abstract base class for backend to simplify code coverage

* Reordered try except block

* Added explicit thread safety

* Fixed linting error

* Worked on redis init block

* Fixed async test setup

* Added tests for redis instantiation

* Fixed linting errors

AUTHORS

@@ -32,6 +32,7 @@ Merijn Bertels <merijn.bertels@gmail.com>
 Omer Katz <omer.drow@gmail.com>
 Petr Knap <dev@petrknap.cz>
 Philip Neustrom <philipn@gmail.com>
+Philipp Thumfart <philipp@thumfart.eu>
 Pierre-Olivier Marec <pomarec@free.fr>
 Roman Krejcik <farin@farin.cz>
 Silvan Spross <silvan.spross@gmail.com>

constance/backends/__init__.py

@@ -1,21 +1,48 @@
 """Defines the base constance backend."""
 
+from abc import ABC
+from abc import abstractmethod
 
-class Backend:
+
+class Backend(ABC):
+    @abstractmethod
     def get(self, key):
         """
         Get the key from the backend store and return the value.
         Return None if not found.
         """
-        raise NotImplementedError
+        ...
 
+    @abstractmethod
+    async def aget(self, key):
+        """
+        Get the key from the backend store and return the value.
+        Return None if not found.
+        """
+        ...
+
+    @abstractmethod
     def mget(self, keys):
         """
         Get the keys from the backend store and return a list of the values.
         Return an empty list if not found.
         """
-        raise NotImplementedError
+        ...
 
+    @abstractmethod
+    async def amget(self, keys):
+        """
+        Get the keys from the backend store and return a list of the values.
+        Return an empty list if not found.
+        """
+        ...
+
+    @abstractmethod
     def set(self, key, value):
         """Add the value to the backend store given the key."""
-        raise NotImplementedError
+        ...
+
+    @abstractmethod
+    async def aset(self, key, value):
+        """Add the value to the backend store given the key."""
+        ...

constance/backends/database.py

@@ -85,6 +85,46 @@ class DatabaseBackend(Backend):
                     self._cache.add(key, value)
         return value
 
+    async def aget(self, key):
+        from asgiref.sync import sync_to_async
+
+        prefixed_key = self.add_prefix(key)
+        value = None
+        if self._cache:
+            value = await self._cache.aget(prefixed_key)
+            if value is None:
+                await sync_to_async(self.autofill, thread_sensitive=True)()
+                value = await self._cache.aget(prefixed_key)
+        if value is None:
+            match = await self._model._default_manager.filter(key=prefixed_key).only("value").afirst()
+            if match:
+                value = loads(match.value)
+                if self._cache:
+                    await self._cache.aadd(prefixed_key, value)
+        return value
+
+    async def amget(self, keys):
+        if not keys:
+            return {}
+
+        prefixed_keys_map = {self.add_prefix(key): key for key in keys}
+        results = {}
+
+        if self._cache:
+            cache_results = await self._cache.aget_many(prefixed_keys_map.keys())
+            for prefixed_key, value in cache_results.items():
+                results[prefixed_keys_map[prefixed_key]] = value
+
+        missing_prefixed_keys = [k for k in prefixed_keys_map if prefixed_keys_map[k] not in results]
+        if missing_prefixed_keys:
+            try:
+                async for const in self._model._default_manager.filter(key__in=missing_prefixed_keys):
+                    results[prefixed_keys_map[const.key]] = loads(const.value)
+            except (OperationalError, ProgrammingError):
+                pass
+
+        return results
+
     def set(self, key, value):
         key = self.add_prefix(key)
         created = False
@@ -119,6 +159,13 @@ class DatabaseBackend(Backend):
 
         signals.config_updated.send(sender=config, key=key, old_value=old_value, new_value=value)
 
+    async def aset(self, key, value):
+        from asgiref.sync import sync_to_async
+
+        # We use sync_to_async because Django's transaction.atomic() and database connections are thread-local.
+        # This ensures the operation runs in the correct database thread until native async transactions are supported.
+        return await sync_to_async(self.set, thread_sensitive=True)(key, value)
+
     def clear(self, sender, instance, created, **kwargs):
         if self._cache and not created:
             keys = [self.add_prefix(k) for k in settings.CONFIG]

constance/backends/memory.py

@@ -19,6 +19,10 @@ class MemoryBackend(Backend):
         with self._lock:
             return self._storage.get(key)
 
+    async def aget(self, key):
+        # Memory operations are fast enough that we don't need true async here
+        return self.get(key)
+
     def mget(self, keys):
         if not keys:
             return None
@@ -30,8 +34,18 @@ class MemoryBackend(Backend):
                     result.append((key, value))
         return result
 
+    async def amget(self, keys):
+        if not keys:
+            return {}
+        with self._lock:
+            return {key: self._storage[key] for key in keys if key in self._storage}
+
     def set(self, key, value):
         with self._lock:
             old_value = self._storage.get(key)
             self._storage[key] = value
             signals.config_updated.send(sender=config, key=key, old_value=old_value, new_value=value)
+
+    async def aset(self, key, value):
+        # Memory operations are fast enough that we don't need true async here
+        self.set(key, value)

constance/backends/redisd.py

@@ -1,3 +1,4 @@
+import asyncio
 from threading import RLock
 from time import monotonic
 
@@ -17,27 +18,59 @@ class RedisBackend(Backend):
         super().__init__()
         self._prefix = settings.REDIS_PREFIX
         connection_cls = settings.REDIS_CONNECTION_CLASS
-        if connection_cls is not None:
+        async_connection_cls = settings.REDIS_ASYNC_CONNECTION_CLASS
+
+        if connection_cls:
             self._rd = utils.import_module_attr(connection_cls)()
         else:
             try:
                 import redis
             except ImportError:
                 raise ImproperlyConfigured("The Redis backend requires redis-py to be installed.") from None
+            else:
                 if isinstance(settings.REDIS_CONNECTION, str):
                     self._rd = redis.from_url(settings.REDIS_CONNECTION)
                 else:
                     self._rd = redis.Redis(**settings.REDIS_CONNECTION)
 
+        if async_connection_cls:
+            self._ard = utils.import_module_attr(async_connection_cls)()
+        else:
+            try:
+                import redis.asyncio as aredis
+            except ImportError:
+                # We set this to none instead of raising an error to indicate that async support is not available
+                # without breaking existing sync usage.
+                self._ard = None
+            else:
+                if isinstance(settings.REDIS_CONNECTION, str):
+                    self._ard = aredis.from_url(settings.REDIS_CONNECTION)
+                else:
+                    self._ard = aredis.Redis(**settings.REDIS_CONNECTION)
+
     def add_prefix(self, key):
         return f"{self._prefix}{key}"
 
+    def _check_async_support(self):
+        if self._ard is None:
+            raise ImproperlyConfigured(
+                "Async support for the Redis backend requires redis>=4.2.0 "
+                "or a custom CONSTANCE_REDIS_ASYNC_CONNECTION_CLASS to be configured."
+            )
+
     def get(self, key):
         value = self._rd.get(self.add_prefix(key))
         if value:
             return loads(value)
         return None
 
+    async def aget(self, key):
+        self._check_async_support()
+        value = await self._ard.get(self.add_prefix(key))
+        if value:
+            return loads(value)
+        return None
+
     def mget(self, keys):
         if not keys:
             return
@@ -46,15 +79,37 @@ class RedisBackend(Backend):
             if value:
                 yield key, loads(value)
 
+    async def amget(self, keys):
+        if not keys:
+            return {}
+        self._check_async_support()
+        prefixed_keys = [self.add_prefix(key) for key in keys]
+        values = await self._ard.mget(prefixed_keys)
+        return {key: loads(value) for key, value in zip(keys, values) if value}
+
     def set(self, key, value):
         old_value = self.get(key)
         self._rd.set(self.add_prefix(key), dumps(value))
         signals.config_updated.send(sender=config, key=key, old_value=old_value, new_value=value)
 
+    async def _aset_internal(self, key, value, old_value):
+        """
+        Internal set operation. Separated to allow subclasses to provide old_value
+        without going through self.aget() which may have locking behavior.
+        """
+        self._check_async_support()
+        await self._ard.set(self.add_prefix(key), dumps(value))
+        signals.config_updated.send(sender=config, key=key, old_value=old_value, new_value=value)
+
+    async def aset(self, key, value):
+        old_value = await self.aget(key)
+        await self._aset_internal(key, value, old_value)
+
 
 class CachingRedisBackend(RedisBackend):
     _sentinel = object()
     _lock = RLock()
+    _async_lock = None  # Lazy-initialized asyncio.Lock
 
     def __init__(self):
         super().__init__()
@@ -62,6 +117,12 @@ class CachingRedisBackend(RedisBackend):
         self._cache = {}
         self._sentinel = object()
 
+    def _get_async_lock(self):
+        # Lazily create the asyncio lock to avoid issues with event loops
+        if self._async_lock is None:
+            self._async_lock = asyncio.Lock()
+        return self._async_lock
+
     def _has_expired(self, value):
         return value[0] <= monotonic()
 
@@ -79,11 +140,41 @@ class CachingRedisBackend(RedisBackend):
 
         return value[1]
 
+    async def _aget_unlocked(self, key):
+        """
+        Get value with cache support but without acquiring lock.
+        Caller must already hold the lock.
+        """
+        value = self._cache.get(key, self._sentinel)
+        if value is self._sentinel or self._has_expired(value):
+            new_value = await super().aget(key)
+            self._cache_value(key, new_value)
+            return new_value
+        return value[1]
+
+    async def aget(self, key):
+        value = self._cache.get(key, self._sentinel)
+
+        if value is self._sentinel or self._has_expired(value):
+            async with self._get_async_lock():
+                # Double-check after acquiring lock, then delegate to unlocked version
+                return await self._aget_unlocked(key)
+
+        return value[1]
+
     def set(self, key, value):
         with self._lock:
             super().set(key, value)
             self._cache_value(key, value)
 
+    async def aset(self, key, value):
+        async with self._get_async_lock():
+            # Use unlocked version since we already hold the lock
+            old_value = await self._aget_unlocked(key)
+            # Use internal method to avoid lock recursion (super().aset calls self.aget)
+            await self._aset_internal(key, value, old_value)
+            self._cache_value(key, value)
+
     def mget(self, keys):
         if not keys:
             return
@@ -91,3 +182,38 @@ class CachingRedisBackend(RedisBackend):
             value = self.get(key)
             if value is not None:
                 yield key, value
+
+    async def amget(self, keys):
+        if not keys:
+            return {}
+
+        results = {}
+        missing_keys = []
+
+        # First, check the local cache for all keys
+        for key in keys:
+            value = self._cache.get(key, self._sentinel)
+            if value is not self._sentinel and not self._has_expired(value):
+                results[key] = value[1]
+            else:
+                missing_keys.append(key)
+
+        # Fetch missing keys from Redis
+        if missing_keys:
+            async with self._get_async_lock():
+                # Re-check cache for keys that might have been fetched while waiting for lock
+                still_missing = []
+                for key in missing_keys:
+                    value = self._cache.get(key, self._sentinel)
+                    if value is not self._sentinel and not self._has_expired(value):
+                        results[key] = value[1]
+                    else:
+                        still_missing.append(key)
+
+                if still_missing:
+                    fetched = await super().amget(still_missing)
+                    for key, value in fetched.items():
+                        self._cache_value(key, value)
+                        results[key] = value
+
+        return results

constance/base.py

@@ -1,31 +1,149 @@
+import asyncio
+import warnings
+
 from . import settings
 from . import utils
 
 
+class AsyncValueProxy:
+    def __init__(self, key, config, default):
+        self._key = key
+        self._config = config
+        self._default = default
+        self._value = None
+        self._fetched = False
+
+    def __await__(self):
+        return self._get_value().__await__()
+
+    async def _get_value(self):
+        if not self._fetched:
+            result = await self._config._backend.aget(self._key)
+            if result is None:
+                result = self._default
+                await self._config.aset(self._key, result)
+            self._value = result
+            self._fetched = True
+        return self._value
+
+    def _get_sync_value(self):
+        warnings.warn(
+            f"Synchronous access to Constance setting '{self._key}' inside an async loop. "
+            f"Use 'await config.{self._key}' instead.",
+            RuntimeWarning,
+            stacklevel=3,
+        )
+        return self._config._get_sync_value(self._key, self._default)
+
+    def __str__(self):
+        return str(self._get_sync_value())
+
+    def __repr__(self):
+        return repr(self._get_sync_value())
+
+    def __int__(self):
+        return int(self._get_sync_value())
+
+    def __float__(self):
+        return float(self._get_sync_value())
+
+    def __bool__(self):
+        return bool(self._get_sync_value())
+
+    def __eq__(self, other):
+        return self._get_sync_value() == other
+
+    def __ne__(self, other):
+        return self._get_sync_value() != other
+
+    def __lt__(self, other):
+        return self._get_sync_value() < other
+
+    def __le__(self, other):
+        return self._get_sync_value() <= other
+
+    def __gt__(self, other):
+        return self._get_sync_value() > other
+
+    def __ge__(self, other):
+        return self._get_sync_value() >= other
+
+    def __getitem__(self, key):
+        return self._get_sync_value()[key]
+
+    def __iter__(self):
+        return iter(self._get_sync_value())
+
+    def __len__(self):
+        return len(self._get_sync_value())
+
+    def __contains__(self, item):
+        return item in self._get_sync_value()
+
+    def __hash__(self):
+        return hash(self._get_sync_value())
+
+    def __add__(self, other):
+        return self._get_sync_value() + other
+
+    def __sub__(self, other):
+        return self._get_sync_value() - other
+
+    def __mul__(self, other):
+        return self._get_sync_value() * other
+
+    def __truediv__(self, other):
+        return self._get_sync_value() / other
+
+
 class Config:
     """The global config wrapper that handles the backend."""
 
     def __init__(self):
         super().__setattr__("_backend", utils.import_module_attr(settings.BACKEND)())
 
+    def _get_sync_value(self, key, default):
+        result = self._backend.get(key)
+        if result is None:
+            result = default
+            setattr(self, key, default)
+        return result
+
     def __getattr__(self, key):
+        if key == "_backend":
+            return super().__getattribute__(key)
         try:
             if len(settings.CONFIG[key]) not in (2, 3):
                 raise AttributeError(key)
             default = settings.CONFIG[key][0]
         except KeyError as e:
             raise AttributeError(key) from e
-        result = self._backend.get(key)
-        if result is None:
-            result = default
-            setattr(self, key, default)
-            return result
-        return result
+
+        try:
+            asyncio.get_running_loop()
+        except RuntimeError:
+            return self._get_sync_value(key, default)
+        return AsyncValueProxy(key, self, default)
 
     def __setattr__(self, key, value):
+        if key == "_backend":
+            super().__setattr__(key, value)
+            return
         if key not in settings.CONFIG:
             raise AttributeError(key)
         self._backend.set(key, value)
+        return
+
+    async def aset(self, key, value):
+        if key not in settings.CONFIG:
+            raise AttributeError(key)
+        await self._backend.aset(key, value)
+
+    async def amget(self, keys):
+        backend_values = await self._backend.amget(keys)
+        # Merge with defaults like utils.get_values_for_keys
+        default_initial = {name: settings.CONFIG[name][0] for name in keys if name in settings.CONFIG}
+        return dict(default_initial, **backend_values)
 
     def __dir__(self):
         return settings.CONFIG.keys()

constance/settings.py

@@ -22,6 +22,8 @@ REDIS_CACHE_TIMEOUT = getattr(settings, "CONSTANCE_REDIS_CACHE_TIMEOUT", 60)
 
 REDIS_CONNECTION_CLASS = getattr(settings, "CONSTANCE_REDIS_CONNECTION_CLASS", None)
 
+REDIS_ASYNC_CONNECTION_CLASS = getattr(settings, "CONSTANCE_REDIS_ASYNC_CONNECTION_CLASS", None)
+
 REDIS_CONNECTION = getattr(settings, "CONSTANCE_REDIS_CONNECTION", {})
 
 SUPERUSER_ONLY = getattr(settings, "CONSTANCE_SUPERUSER_ONLY", True)

constance/utils.py

@@ -22,6 +22,16 @@ def get_values():
     return dict(default_initial, **dict(config._backend.mget(settings.CONFIG)))
 
 
+async def aget_values():
+    """
+    Get dictionary of values from the backend asynchronously
+    :return:
+    """
+    default_initial = {name: options[0] for name, options in settings.CONFIG.items()}
+    backend_values = await config.amget(settings.CONFIG.keys())
+    return dict(default_initial, **backend_values)
+
+
 def get_values_for_keys(keys):
     """
     Retrieve values for specified keys from the backend.
@@ -43,3 +53,24 @@ def get_values_for_keys(keys):
 
     # Merge default values and backend values, prioritizing backend values
     return dict(default_initial, **dict(config._backend.mget(keys)))
+
+
+async def aget_values_for_keys(keys):
+    """
+    Retrieve values for specified keys from the backend asynchronously.
+
+    :param keys: List of keys to retrieve.
+    :return: Dictionary with values for the specified keys.
+    :raises AttributeError: If any key is not found in the configuration.
+    """
+    if not isinstance(keys, (list, tuple, set)):
+        raise TypeError("keys must be a list, tuple, or set of strings")
+
+    default_initial = {name: options[0] for name, options in settings.CONFIG.items() if name in keys}
+
+    missing_keys = [key for key in keys if key not in default_initial]
+    if missing_keys:
+        raise AttributeError(f'"{", ".join(missing_keys)}" keys not found in configuration.')
+
+    backend_values = await config.amget(keys)
+    return dict(default_initial, **backend_values)

docs/conf.py

@@ -11,10 +11,11 @@ from datetime import datetime
 def get_version():
     # Try to get version from installed package metadata
     try:
+        from importlib.metadata import PackageNotFoundError
         from importlib.metadata import version
 
         return version("django-constance")
-    except Exception:
+    except (ImportError, PackageNotFoundError):
         pass
 
     # Fall back to setuptools_scm generated version file

docs/index.rst

@@ -292,6 +292,36 @@ object and accessing the variables with attribute lookups::
     if config.THE_ANSWER == 42:
         answer_the_question()
 
+Asynchronous usage
+^^^^^^^^^^^^^^^^^^
+
+If you are using Django's asynchronous features (like async views), you can ``await`` the settings directly on the standard ``config`` object::
+
+    from constance import config
+
+    async def my_async_view(request):
+        # Accessing settings is awaitable
+        if await config.THE_ANSWER == 42:
+            return await answer_the_question_async()
+
+    async def update_settings():
+        # Updating settings asynchronously
+        await config.aset('THE_ANSWER', 43)
+
+        # Bulk retrieval is supported as well
+        values = await config.amget(['THE_ANSWER', 'SITE_NAME'])
+
+Performance and Safety
+~~~~~~~~~~~~~~~~~~~~~~
+
+While synchronous access (e.g., ``config.THE_ANSWER``) still works inside async views for some backends, it is highly discouraged:
+
+*   **Blocking:** Synchronous access blocks the event loop, reducing the performance of your entire application.
+*   **Safety Guards:** For the Database backend, Django's safety guards will raise a ``SynchronousOnlyOperation`` error if you attempt to access a setting synchronously from an async thread.
+*   **Automatic Detection:** Constance will emit a ``RuntimeWarning`` if it detects synchronous access inside an asynchronous event loop, helping you identify and fix these performance bottlenecks.
+
+For peak performance, especially with the Redis backend, always use the ``await`` syntax which leverages native asynchronous drivers.
+
 Django templates
 ^^^^^^^^^^^^^^^^
 

tests/backends/test_database.py

@@ -1,6 +1,8 @@
 from django.test import TestCase
+from django.test import TransactionTestCase
 
 from constance import settings
+from constance.base import Config
 from tests.storage import StorageTestsMixin
 
 
@@ -52,3 +54,95 @@ class TestDatabaseWithCache(StorageTestsMixin, TestCase):
     def tearDown(self):
         settings.BACKEND = self.old_backend
         settings.DATABASE_CACHE_BACKEND = self.old_cache_backend
+
+
+class TestDatabaseAsync(TransactionTestCase):
+    def setUp(self):
+        self.old_backend = settings.BACKEND
+        settings.BACKEND = "constance.backends.database.DatabaseBackend"
+        self.config = Config()
+
+    def tearDown(self):
+        settings.BACKEND = self.old_backend
+
+    async def test_aget_returns_none_for_missing_key(self):
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertIsNone(result)
+
+    async def test_aget_returns_value(self):
+        await self.config._backend.aset("INT_VALUE", 42)
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertEqual(result, 42)
+
+    async def test_aset_stores_value(self):
+        await self.config._backend.aset("INT_VALUE", 99)
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertEqual(result, 99)
+
+    async def test_amget_returns_empty_for_no_keys(self):
+        result = await self.config._backend.amget([])
+        self.assertEqual(result, {})
+
+    async def test_amget_returns_values(self):
+        await self.config._backend.aset("INT_VALUE", 10)
+        await self.config._backend.aset("BOOL_VALUE", value=True)
+        result = await self.config._backend.amget(["INT_VALUE", "BOOL_VALUE"])
+        self.assertEqual(result, {"INT_VALUE": 10, "BOOL_VALUE": True})
+
+
+class TestDatabaseWithCacheAsync(TransactionTestCase):
+    def setUp(self):
+        self.old_backend = settings.BACKEND
+        settings.BACKEND = "constance.backends.database.DatabaseBackend"
+        self.old_cache_backend = settings.DATABASE_CACHE_BACKEND
+        settings.DATABASE_CACHE_BACKEND = "default"
+        self.config = Config()
+        self.config._backend._cache.clear()
+
+    def tearDown(self):
+        settings.BACKEND = self.old_backend
+        settings.DATABASE_CACHE_BACKEND = self.old_cache_backend
+
+    async def test_aget_returns_none_for_missing_key(self):
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertIsNone(result)
+
+    async def test_aget_returns_value_from_cache(self):
+        # First set a value using async
+        await self.config._backend.aset("INT_VALUE", 42)
+        # Clear cache and re-fetch to test aget path
+        self.config._backend._cache.clear()
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertEqual(result, 42)
+
+    async def test_aget_populates_cache(self):
+        await self.config._backend.aset("INT_VALUE", 42)
+        self.config._backend._cache.clear()
+
+        # aget should populate the cache
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertEqual(result, 42)
+
+    async def test_aset_stores_value(self):
+        await self.config._backend.aset("INT_VALUE", 99)
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertEqual(result, 99)
+
+    async def test_amget_returns_empty_for_no_keys(self):
+        result = await self.config._backend.amget([])
+        self.assertEqual(result, {})
+
+    async def test_amget_returns_values(self):
+        await self.config._backend.aset("INT_VALUE", 10)
+        await self.config._backend.aset("BOOL_VALUE", value=True)
+        result = await self.config._backend.amget(["INT_VALUE", "BOOL_VALUE"])
+        self.assertEqual(result, {"INT_VALUE": 10, "BOOL_VALUE": True})
+
+    async def test_amget_uses_cache(self):
+        # Set values using async and ensure they're cached
+        await self.config._backend.aset("INT_VALUE", 10)
+        await self.config._backend.aset("BOOL_VALUE", value=True)
+
+        result = await self.config._backend.amget(["INT_VALUE", "BOOL_VALUE"])
+        self.assertEqual(result["INT_VALUE"], 10)
+        self.assertEqual(result["BOOL_VALUE"], True)

tests/backends/test_memory.py

@@ -1,6 +1,8 @@
 from django.test import TestCase
+from django.test import TransactionTestCase
 
 from constance import settings
+from constance.base import Config
 from tests.storage import StorageTestsMixin
 
 
@@ -14,3 +16,43 @@ class TestMemory(StorageTestsMixin, TestCase):
     def tearDown(self):
         self.config._backend._storage = {}
         settings.BACKEND = self.old_backend
+
+    def test_mget_empty_keys(self):
+        result = self.config._backend.mget([])
+        self.assertIsNone(result)
+
+
+class TestMemoryAsync(TransactionTestCase):
+    def setUp(self):
+        self.old_backend = settings.BACKEND
+        settings.BACKEND = "constance.backends.memory.MemoryBackend"
+        self.config = Config()
+        self.config._backend._storage = {}
+
+    def tearDown(self):
+        self.config._backend._storage = {}
+        settings.BACKEND = self.old_backend
+
+    async def test_aget_returns_none_for_missing_key(self):
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertIsNone(result)
+
+    async def test_aget_returns_value(self):
+        self.config._backend.set("INT_VALUE", 42)
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertEqual(result, 42)
+
+    async def test_aset_stores_value(self):
+        await self.config._backend.aset("INT_VALUE", 99)
+        result = self.config._backend.get("INT_VALUE")
+        self.assertEqual(result, 99)
+
+    async def test_amget_returns_empty_for_no_keys(self):
+        result = await self.config._backend.amget([])
+        self.assertEqual(result, {})
+
+    async def test_amget_returns_values(self):
+        self.config._backend.set("INT_VALUE", 10)
+        self.config._backend.set("BOOL_VALUE", value=True)
+        result = await self.config._backend.amget(["INT_VALUE", "BOOL_VALUE"])
+        self.assertEqual(result, {"INT_VALUE": 10, "BOOL_VALUE": True})

tests/backends/test_redis.py

@@ -1,6 +1,12 @@
+from unittest import mock
+
+from django.core.exceptions import ImproperlyConfigured
 from django.test import TestCase
+from django.test import TransactionTestCase
 
 from constance import settings
+from constance.backends.redisd import RedisBackend
+from constance.base import Config
 from tests.storage import StorageTestsMixin
 
 
@@ -17,6 +23,241 @@ class TestRedis(StorageTestsMixin, TestCase):
         self.config._backend._rd.clear()
         settings.BACKEND = self.old_backend
 
+    def test_mget_empty_keys(self):
+        # Test that mget returns None for empty keys
+        result = list(self.config._backend.mget([]) or [])
+        self.assertEqual(result, [])
+
 
 class TestCachingRedis(TestRedis):
     _BACKEND = "constance.backends.redisd.CachingRedisBackend"
+
+    def test_mget_empty_keys(self):
+        # Test that mget returns None for empty keys
+        result = list(self.config._backend.mget([]) or [])
+        self.assertEqual(result, [])
+
+
+class TestRedisAsync(TransactionTestCase):
+    _BACKEND = "constance.backends.redisd.RedisBackend"
+
+    def setUp(self):
+        self.old_backend = settings.BACKEND
+        settings.BACKEND = self._BACKEND
+        self.config = Config()
+        self.config._backend._rd.clear()
+
+    def tearDown(self):
+        self.config._backend._rd.clear()
+        settings.BACKEND = self.old_backend
+
+    async def test_aget_returns_none_for_missing_key(self):
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertIsNone(result)
+
+    async def test_aget_returns_value(self):
+        self.config._backend.set("INT_VALUE", 42)
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertEqual(result, 42)
+
+    async def test_aset_stores_value(self):
+        await self.config._backend.aset("INT_VALUE", 99)
+        result = self.config._backend.get("INT_VALUE")
+        self.assertEqual(result, 99)
+
+    async def test_amget_returns_empty_for_no_keys(self):
+        result = await self.config._backend.amget([])
+        self.assertEqual(result, {})
+
+    async def test_amget_returns_values(self):
+        self.config._backend.set("INT_VALUE", 10)
+        self.config._backend.set("BOOL_VALUE", value=True)
+        result = await self.config._backend.amget(["INT_VALUE", "BOOL_VALUE"])
+        self.assertEqual(result, {"INT_VALUE": 10, "BOOL_VALUE": True})
+
+    async def test_amget_skips_missing_keys(self):
+        self.config._backend.set("INT_VALUE", 10)
+        result = await self.config._backend.amget(["INT_VALUE", "MISSING_KEY"])
+        self.assertEqual(result, {"INT_VALUE": 10})
+
+
+class TestCachingRedisAsync(TransactionTestCase):
+    _BACKEND = "constance.backends.redisd.CachingRedisBackend"
+
+    def setUp(self):
+        self.old_backend = settings.BACKEND
+        settings.BACKEND = self._BACKEND
+        self.config = Config()
+        self.config._backend._rd.clear()
+        self.config._backend._cache.clear()
+
+    def tearDown(self):
+        self.config._backend._rd.clear()
+        self.config._backend._cache.clear()
+        settings.BACKEND = self.old_backend
+
+    async def test_aget_caches_value(self):
+        # First set a value via sync
+        self.config._backend.set("INT_VALUE", 42)
+        # Clear the in-memory cache
+        self.config._backend._cache.clear()
+
+        # Async get should fetch and cache
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertEqual(result, 42)
+
+        # Verify it's cached
+        self.assertIn("INT_VALUE", self.config._backend._cache)
+
+    async def test_aget_returns_cached_value(self):
+        # Manually set cache
+        from time import monotonic
+
+        timeout = self.config._backend._timeout
+        self.config._backend._cache["INT_VALUE"] = (monotonic() + timeout, 100)
+
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertEqual(result, 100)
+
+    async def test_aget_refreshes_expired_cache(self):
+        from time import monotonic
+
+        # Set expired cache
+        self.config._backend._cache["INT_VALUE"] = (monotonic() - 10, 100)
+        # Set different value in redis using proper codec format
+        self.config._backend._rd.set(
+            self.config._backend.add_prefix("INT_VALUE"),
+            b'{"__type__": "default", "__value__": 200}',
+        )
+
+        result = await self.config._backend.aget("INT_VALUE")
+        self.assertEqual(result, 200)
+
+    async def test_aset_updates_cache(self):
+        await self.config._backend.aset("INT_VALUE", 55)
+
+        # Verify cache is updated
+        self.assertIn("INT_VALUE", self.config._backend._cache)
+        self.assertEqual(self.config._backend._cache["INT_VALUE"][1], 55)
+
+    async def test_amget_returns_empty_for_no_keys(self):
+        result = await self.config._backend.amget([])
+        self.assertEqual(result, {})
+
+    async def test_amget_returns_cached_values(self):
+        from time import monotonic
+
+        timeout = self.config._backend._timeout
+        self.config._backend._cache["INT_VALUE"] = (monotonic() + timeout, 10)
+        self.config._backend._cache["BOOL_VALUE"] = (monotonic() + timeout, True)
+
+        result = await self.config._backend.amget(["INT_VALUE", "BOOL_VALUE"])
+        self.assertEqual(result, {"INT_VALUE": 10, "BOOL_VALUE": True})
+
+    async def test_amget_fetches_missing_keys(self):
+        from time import monotonic
+
+        timeout = self.config._backend._timeout
+        # One key cached, one in Redis only
+        self.config._backend._cache["INT_VALUE"] = (monotonic() + timeout, 10)
+        self.config._backend._rd.set(
+            self.config._backend.add_prefix("BOOL_VALUE"),
+            b'{"__type__": "default", "__value__": true}',
+        )
+
+        result = await self.config._backend.amget(["INT_VALUE", "BOOL_VALUE"])
+        self.assertEqual(result["INT_VALUE"], 10)
+        self.assertEqual(result["BOOL_VALUE"], True)
+
+    async def test_amget_refreshes_expired_keys(self):
+        from time import monotonic
+
+        # Set expired cache
+        self.config._backend._cache["INT_VALUE"] = (monotonic() - 10, 100)
+        # Set different value in redis using proper codec format
+        self.config._backend._rd.set(
+            self.config._backend.add_prefix("INT_VALUE"),
+            b'{"__type__": "default", "__value__": 200}',
+        )
+
+        result = await self.config._backend.amget(["INT_VALUE"])
+        self.assertEqual(result["INT_VALUE"], 200)
+
+
+class TestRedisBackendInit(TestCase):
+    """Tests for RedisBackend.__init__ client initialization paths."""
+
+    def setUp(self):
+        self.old_conn_cls = settings.REDIS_CONNECTION_CLASS
+        self.old_async_conn_cls = settings.REDIS_ASYNC_CONNECTION_CLASS
+        self.old_conn = settings.REDIS_CONNECTION
+
+    def tearDown(self):
+        settings.REDIS_CONNECTION_CLASS = self.old_conn_cls
+        settings.REDIS_ASYNC_CONNECTION_CLASS = self.old_async_conn_cls
+        settings.REDIS_CONNECTION = self.old_conn
+
+    def test_no_redis_package_raises_improperly_configured(self):
+        settings.REDIS_CONNECTION_CLASS = None
+        settings.REDIS_ASYNC_CONNECTION_CLASS = "tests.redis_mockup.AsyncConnection"
+        with mock.patch.dict("sys.modules", {"redis": None}), self.assertRaises(ImproperlyConfigured):
+            RedisBackend()
+
+    def test_sync_redis_from_url_with_string_connection(self):
+        settings.REDIS_CONNECTION_CLASS = None
+        settings.REDIS_ASYNC_CONNECTION_CLASS = "tests.redis_mockup.AsyncConnection"
+        settings.REDIS_CONNECTION = "redis://localhost:6379/0"
+        mock_redis = mock.MagicMock()
+        with mock.patch.dict("sys.modules", {"redis": mock_redis, "redis.asyncio": mock_redis.asyncio}):
+            backend = RedisBackend()
+        mock_redis.from_url.assert_called_once_with("redis://localhost:6379/0")
+        self.assertEqual(backend._rd, mock_redis.from_url.return_value)
+
+    def test_sync_redis_with_dict_connection(self):
+        settings.REDIS_CONNECTION_CLASS = None
+        settings.REDIS_ASYNC_CONNECTION_CLASS = "tests.redis_mockup.AsyncConnection"
+        settings.REDIS_CONNECTION = {"host": "localhost", "port": 6379}
+        mock_redis = mock.MagicMock()
+        with mock.patch.dict("sys.modules", {"redis": mock_redis, "redis.asyncio": mock_redis.asyncio}):
+            backend = RedisBackend()
+        mock_redis.Redis.assert_called_once_with(host="localhost", port=6379)
+        self.assertEqual(backend._rd, mock_redis.Redis.return_value)
+
+    def test_async_redis_not_available_sets_ard_none(self):
+        settings.REDIS_CONNECTION_CLASS = "tests.redis_mockup.Connection"
+        settings.REDIS_ASYNC_CONNECTION_CLASS = None
+        mock_redis = mock.MagicMock()
+        # Simulate redis.asyncio not being available
+        with mock.patch.dict("sys.modules", {"redis": mock_redis, "redis.asyncio": None}):
+            backend = RedisBackend()
+        self.assertIsNone(backend._ard)
+
+    def test_async_redis_from_url_with_string_connection(self):
+        settings.REDIS_CONNECTION_CLASS = "tests.redis_mockup.Connection"
+        settings.REDIS_ASYNC_CONNECTION_CLASS = None
+        settings.REDIS_CONNECTION = "redis://localhost:6379/0"
+        mock_aredis = mock.MagicMock()
+        mock_redis = mock.MagicMock()
+        mock_redis.asyncio = mock_aredis
+        with mock.patch.dict("sys.modules", {"redis": mock_redis, "redis.asyncio": mock_aredis}):
+            backend = RedisBackend()
+        mock_aredis.from_url.assert_called_once_with("redis://localhost:6379/0")
+        self.assertEqual(backend._ard, mock_aredis.from_url.return_value)
+
+    def test_async_redis_with_dict_connection(self):
+        settings.REDIS_CONNECTION_CLASS = "tests.redis_mockup.Connection"
+        settings.REDIS_ASYNC_CONNECTION_CLASS = None
+        settings.REDIS_CONNECTION = {"host": "localhost", "port": 6379}
+        mock_aredis = mock.MagicMock()
+        mock_redis = mock.MagicMock()
+        mock_redis.asyncio = mock_aredis
+        with mock.patch.dict("sys.modules", {"redis": mock_redis, "redis.asyncio": mock_aredis}):
+            backend = RedisBackend()
+        mock_aredis.Redis.assert_called_once_with(host="localhost", port=6379)
+        self.assertEqual(backend._ard, mock_aredis.Redis.return_value)
+
+    def test_check_async_support_raises_when_ard_is_none(self):
+        backend = RedisBackend()
+        backend._ard = None
+        with self.assertRaises(ImproperlyConfigured):
+            backend._check_async_support()

tests/cache_mockup.py

@@ -10,3 +10,16 @@ class Cache(BaseCache):
         self.set = self._cache.set
         self.get = self._cache.get
         self.clear = self._cache.clear
+        self.set_many = self._cache.set_many
+        self.get_many = self._cache.get_many
+        self.delete_many = self._cache.delete_many
+
+    # Async methods for DatabaseBackend.aget() support
+    async def aget(self, key, default=None, version=None):
+        return self.get(key, default, version)
+
+    async def aget_many(self, keys, version=None):
+        return self.get_many(keys, version)
+
+    async def aadd(self, key, value, timeout=None, version=None):
+        return self.add(key, value, timeout, version)

tests/redis_mockup.py

@@ -1,6 +1,28 @@
-class Connection(dict):
+# Shared storage so sync (Connection) and async (AsyncConnection) instances
+# operate on the same underlying data, just like a real Redis server would.
+_shared_store = {}
+
+
+class Connection:
     def set(self, key, value):
-        self[key] = value
+        _shared_store[key] = value
+
+    def get(self, key, default=None):
+        return _shared_store.get(key, default)
 
     def mget(self, keys):
-        return [self.get(key) for key in keys]
+        return [_shared_store.get(key) for key in keys]
+
+    def clear(self):
+        _shared_store.clear()
+
+
+class AsyncConnection:
+    async def set(self, key, value):
+        _shared_store[key] = value
+
+    async def get(self, key):
+        return _shared_store.get(key)
+
+    async def mget(self, keys):
+        return [_shared_store.get(key) for key in keys]

tests/settings.py

@@ -50,6 +50,7 @@ INSTALLED_APPS = (
 ROOT_URLCONF = "tests.urls"
 
 CONSTANCE_REDIS_CONNECTION_CLASS = "tests.redis_mockup.Connection"
+CONSTANCE_REDIS_ASYNC_CONNECTION_CLASS = "tests.redis_mockup.AsyncConnection"
 
 CONSTANCE_ADDITIONAL_FIELDS = {
     "yes_no_null_select": [

tests/test_async.py

@@ -0,0 +1,198 @@
+import warnings
+
+from django.test import TransactionTestCase
+
+from constance import config
+from constance import utils
+
+
+class AsyncTestCase(TransactionTestCase):
+    async def test_async_get(self):
+        # Accessing an attribute on config should be awaitable when in async context
+        val = await config.INT_VALUE
+        self.assertEqual(val, 1)
+
+    async def test_async_set(self):
+        await config.aset("INT_VALUE", 42)
+        val = await config.INT_VALUE
+        self.assertEqual(val, 42)
+
+        # Verify sync access also works (and emits warning)
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            sync_val = int(config.INT_VALUE)
+            self.assertEqual(sync_val, 42)
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_amget(self):
+        values = await config.amget(["INT_VALUE", "BOOL_VALUE"])
+        self.assertEqual(values["INT_VALUE"], 1)
+        self.assertEqual(values["BOOL_VALUE"], True)
+
+    async def test_sync_math_in_async_loop(self):
+        # Accessing math should work but emit warning
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            res = config.INT_VALUE + 10
+            # Note: res will be 42 + 10 if test_async_set ran before, or 1 + 10 if not.
+            # TransactionTestCase should reset state, but let's be careful.
+            # config.INT_VALUE defaults to 1.
+            self.assertEqual(res, 11 if res < 50 else 52)
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_utils_aget_values(self):
+        values = await utils.aget_values()
+        self.assertIn("INT_VALUE", values)
+        self.assertIn("BOOL_VALUE", values)
+        self.assertEqual(values["INT_VALUE"], 1)
+
+    async def test_utils_aget_values_for_keys(self):
+        values = await utils.aget_values_for_keys(["INT_VALUE"])
+        self.assertEqual(len(values), 1)
+        self.assertEqual(values["INT_VALUE"], 1)
+
+    async def test_bool_proxy(self):
+        # BOOL_VALUE is True by default
+        self.assertTrue(config.BOOL_VALUE)
+
+    async def test_int_proxy(self):
+        await config.aset("INT_VALUE", 1)
+        self.assertEqual(int(config.INT_VALUE), 1)
+
+    async def test_container_proxy(self):
+        # LIST_VALUE is [1, "1", date(2019, 1, 1)] by default
+        self.assertEqual(config.LIST_VALUE[0], 1)
+        self.assertEqual(len(config.LIST_VALUE), 3)
+        self.assertIn(1, config.LIST_VALUE)
+        self.assertEqual(next(iter(config.LIST_VALUE)), 1)
+
+
+class AsyncValueProxyTestCase(TransactionTestCase):
+    """Tests for AsyncValueProxy dunder methods in async context."""
+
+    async def test_str_proxy(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = str(config.STRING_VALUE)
+            self.assertEqual(result, "Hello world")
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_repr_proxy(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = repr(config.STRING_VALUE)
+            self.assertEqual(result, "'Hello world'")
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_float_proxy(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = float(config.FLOAT_VALUE)
+            self.assertAlmostEqual(result, 3.1415926536)
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_eq_proxy(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = config.INT_VALUE == 1
+            self.assertTrue(result)
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_ne_proxy(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = config.INT_VALUE != 2
+            self.assertTrue(result)
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_lt_proxy(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = config.INT_VALUE < 10
+            self.assertTrue(result)
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_le_proxy(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = config.INT_VALUE <= 1
+            self.assertTrue(result)
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_gt_proxy(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = config.INT_VALUE > 0
+            self.assertTrue(result)
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_ge_proxy(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = config.INT_VALUE >= 1
+            self.assertTrue(result)
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_hash_proxy(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = hash(config.INT_VALUE)
+            self.assertEqual(result, hash(1))
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_sub_proxy(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = config.INT_VALUE - 1
+            self.assertEqual(result, 0)
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_mul_proxy(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = config.INT_VALUE * 5
+            self.assertEqual(result, 5)
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_truediv_proxy(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = config.INT_VALUE / 1
+            self.assertEqual(result, 1.0)
+            self.assertTrue(any("Synchronous access" in str(warn.message) for warn in w))
+
+    async def test_aset_invalid_key(self):
+        with self.assertRaises(AttributeError):
+            await config.aset("INVALID_KEY", 42)
+
+
+class AsyncUtilsTestCase(TransactionTestCase):
+    """Tests for async utility functions."""
+
+    async def test_aget_values_for_keys_invalid_type(self):
+        with self.assertRaises(TypeError):
+            await utils.aget_values_for_keys("key1")
+
+    async def test_aget_values_for_keys_missing_key(self):
+        with self.assertRaises(AttributeError) as ctx:
+            await utils.aget_values_for_keys(["INVALID_KEY"])
+        self.assertIn("INVALID_KEY", str(ctx.exception))
+
+    async def test_aget_values_for_keys_empty(self):
+        result = await utils.aget_values_for_keys([])
+        self.assertEqual(result, {})
+
+
+class ConfigBaseTestCase(TransactionTestCase):
+    """Tests for Config class edge cases."""
+
+    def test_config_dir(self):
+        # Test __dir__ method
+        keys = dir(config)
+        self.assertIn("INT_VALUE", keys)
+        self.assertIn("BOOL_VALUE", keys)
+
+    def test_access_backend_attribute(self):
+        # Test accessing _backend attribute in sync context
+        backend = config._backend
+        self.assertIsNotNone(backend)