Introduce skip_cache_func (#652)

Co-authored-by: Vitaly Petrov <[email protected]>
Co-authored-by: Sam Bull <[email protected]>

aiocache/decorators.py

@@ -43,6 +43,10 @@ class cached:
     :param key_builder: Callable that allows to build the function dynamically. It receives
         the function plus same args and kwargs passed to the function.
         This behavior is necessarily different than ``BaseCache.build_key()``
+    :param skip_cache_func: Callable that receives the result after calling the
+        wrapped function and should return `True` if the value should skip the
+        cache (or `False` to store in the cache).
+        e.g. to avoid caching `None` results: `lambda r: r is None`
     :param cache: cache class to use when calling the ``set``/``get`` operations.
         Default is :class:`aiocache.SimpleMemoryCache`.
     :param serializer: serializer instance to use when calling the ``dumps``/``loads``.
@@ -63,6 +67,7 @@ def __init__(
         key=None,
         namespace=None,
         key_builder=None,
+        skip_cache_func=lambda x: False,
         cache=Cache.MEMORY,
         serializer=None,
         plugins=None,
@@ -73,6 +78,7 @@ def __init__(
         self.ttl = ttl
         self.key = key
         self.key_builder = key_builder
+        self.skip_cache_func = skip_cache_func
         self.noself = noself
         self.alias = alias
         self.cache = None
@@ -117,6 +123,9 @@ async def decorator(
 
         result = await f(*args, **kwargs)
 
+        if self.skip_cache_func(result):
+            return result
+
         if cache_write:
             if aiocache_wait_for_write:
                 await self.set_in_cache(key, result)
@@ -182,6 +191,10 @@ class cached_stampede(cached):
     :param key_builder: Callable that allows to build the function dynamically. It receives
         the function plus same args and kwargs passed to the function.
         This behavior is necessarily different than ``BaseCache.build_key()``
+    :param skip_cache_func: Callable that receives the result after calling the
+        wrapped function and should return `True` if the value should skip the
+        cache (or `False` to store in the cache).
+        e.g. to avoid caching `None` results: `lambda r: r is None`
     :param cache: cache class to use when calling the ``set``/``get`` operations.
         Default is :class:`aiocache.SimpleMemoryCache`.
     :param serializer: serializer instance to use when calling the ``dumps``/``loads``.
@@ -213,6 +226,9 @@ async def decorator(self, f, *args, **kwargs):
 
             result = await f(*args, **kwargs)
 
+            if self.skip_cache_func(result):
+                return result
+
             await self.set_in_cache(key, result)
 
         return result
@@ -279,6 +295,9 @@ class multi_cached:
         ``keys_from_attr``, the decorated callable, and the positional and keyword arguments
         that were passed to the decorated callable. This behavior is necessarily different than
         ``BaseCache.build_key()`` and the call signature differs from ``cached.key_builder``.
+    :param skip_cache_keys: Callable that receives both key and value and returns True
+        if that key-value pair should not be cached (or False to store in cache).
+        The keys and values to be passed are taken from the wrapped function result.
     :param ttl: int seconds to store the keys. Default is 0 which means no expiration.
     :param cache: cache class to use when calling the ``multi_set``/``multi_get`` operations.
         Default is :class:`aiocache.SimpleMemoryCache`.
@@ -297,6 +316,7 @@ def __init__(
         keys_from_attr,
         namespace=None,
         key_builder=None,
+        skip_cache_func=lambda k, v: False,
         ttl=SENTINEL,
         cache=Cache.MEMORY,
         serializer=None,
@@ -306,6 +326,7 @@ def __init__(
     ):
         self.keys_from_attr = keys_from_attr
         self.key_builder = key_builder or (lambda key, f, *args, **kwargs: key)
+        self.skip_cache_func = skip_cache_func
         self.ttl = ttl
         self.alias = alias
         self.cache = None
@@ -365,12 +386,17 @@ async def decorator(
         result = await f(*new_args, **kwargs)
         result.update(partial)
 
+        to_cache = {k: v for k, v in result.items() if not self.skip_cache_func(k, v)}
+
+        if not to_cache:
+            return result
+
         if cache_write:
             if aiocache_wait_for_write:
-                await self.set_in_cache(result, f, args, kwargs)
+                await self.set_in_cache(to_cache, f, args, kwargs)
             else:
                 # TODO: Use aiojobs to avoid warnings.
-                asyncio.create_task(self.set_in_cache(result, f, args, kwargs))
+                asyncio.create_task(self.set_in_cache(to_cache, f, args, kwargs))
 
         return result
 

tests/acceptance/test_decorators.py

@@ -49,6 +49,31 @@ async def fn(self, a, b=2):
         await fn("self", 1, 3)
         assert await cache.exists(build_key(fn, "self", 1, 3)) is True
 
+    @pytest.mark.parametrize("decorator", (cached, cached_stampede))
+    async def test_cached_skip_cache_func(self, cache, decorator):
+        @decorator(skip_cache_func=lambda r: r is None)
+        async def sk_func(x):
+            return x if x > 0 else None
+
+        arg = 1
+        res = await sk_func(arg)
+        assert res
+
+        key = decorator().get_cache_key(sk_func, args=(1,), kwargs={})
+
+        assert key
+        assert await cache.exists(key)
+        assert await cache.get(key) == res
+
+        arg = -1
+
+        await sk_func(arg)
+
+        key = decorator().get_cache_key(sk_func, args=(-1,), kwargs={})
+
+        assert key
+        assert not await cache.exists(key)
+
     async def test_cached_without_namespace(self, cache):
         """Default cache key is created when no namespace is provided"""
         @cached(namespace=None)
@@ -149,6 +174,19 @@ async def fn(self, keys, market="ES"):
         assert await cache.exists("fn_" + _ensure_key(Keys.KEY) + "_ES") is True
         assert await cache.exists("fn_" + _ensure_key(Keys.KEY_1) + "_ES") is True
 
+    async def test_multi_cached_skip_keys(self, cache):
+        @multi_cached(keys_from_attr="keys", skip_cache_func=lambda _, v: v is None)
+        async def multi_sk_fn(keys, values):
+            return {k: v for k, v in zip(keys, values)}
+
+        res = await multi_sk_fn(keys=[Keys.KEY, Keys.KEY_1], values=[42, None])
+        assert res
+        assert Keys.KEY in res and Keys.KEY_1 in res
+
+        assert await cache.exists(Keys.KEY)
+        assert await cache.get(Keys.KEY) == res[Keys.KEY]
+        assert not await cache.exists(Keys.KEY_1)
+
     async def test_fn_with_args(self, cache):
         @multi_cached("keys")
         async def fn(keys, *args):