Added add for all backends

README.rst

@@ -23,12 +23,12 @@ Current supported backends are:
 
 This libraries aims for simplicity over specialization. It provides a common interface for all caches which allows to store any python object. The operations supported by all backends are:
 
-- `add`
-- `get`
-- `set`
-- `multi_get`
-- `multi_set`
-- `delete`
+- ``add``
+- ``get``
+- ``set``
+- ``multi_get``
+- ``multi_set``
+- ``delete``
 
 
 Usage

aiocache/backends/base.py

@@ -11,8 +11,9 @@ class BaseCache(metaclass=abc.ABCMeta):
     def get_serializer(self):
         return DefaultSerializer()
 
-    async def add(self, key, value):
-        raise NotImplementedError
+    @abc.abstractmethod
+    async def add(self, key, value, ttl=None):
+        pass
 
     @abc.abstractmethod
     async def get(self, key, default=None):

aiocache/backends/memory.py

@@ -47,7 +47,7 @@ async def set(self, key, value, ttl=None, dumps_fn=None):
         :param value: obj
         :param ttl: int the expiration time in seconds
         :param dumps_fn: callable alternative to use as dumps function
-        :returns:
+        :returns: True
         """
         dumps = dumps_fn or self.serializer.dumps
         SimpleMemoryCache._cache[self._build_key(key)] = dumps(value)
@@ -62,14 +62,39 @@ async def multi_set(self, pairs, dumps_fn=None):
 
         :param pairs: list of two element iterables. First is key and second is value
         :param dumps_fn: callable alternative to use as dumps function
-        :returns:
+        :returns: True
         """
         dumps = dumps_fn or self.serializer.dumps
 
         for key, value in pairs:
             SimpleMemoryCache._cache[self._build_key(key)] = dumps(value)
         return True
 
+    async def add(self, key, value, ttl=None, dumps_fn=None):
+        """
+        Stores the value in the given key with ttl if specified. Raises an error if the
+        key already exists.
+
+        :param key: str
+        :param value: obj
+        :param ttl: int the expiration time in seconds
+        :param dumps_fn: callable alternative to use as dumps function
+        :returns: True if key is inserted
+        :raises: Value error if key already exists
+        """
+        dumps = dumps_fn or self.serializer.dumps
+
+        key = self._build_key(key)
+        if key in SimpleMemoryCache._cache:
+            raise ValueError(
+                "Key {} already exists, use .set to update the value".format(key))
+
+        SimpleMemoryCache._cache[self._build_key(key)] = dumps(value)
+        if ttl:
+            loop = asyncio.get_event_loop()
+            loop.call_later(ttl, self._delete, key)
+        return True
+
     async def delete(self, key):
         """
         Deletes the given key.

aiocache/backends/redis.py

@@ -58,7 +58,7 @@ async def set(self, key, value, ttl=None, dumps_fn=None):
         :param value: obj
         :param ttl: int the expiration time in seconds
         :param dumps_fn: callable alternative to use as dumps function
-        :returns:
+        :returns: True
         """
         dumps = dumps_fn or self.serializer.dumps
         ttl = ttl or 0
@@ -72,7 +72,7 @@ async def multi_set(self, pairs, dumps_fn=None):
 
         :param pairs: list of two element iterables. First is key and second is value
         :param dumps: callable alternative to use as dumps function
-        :returns:
+        :returns: True
         """
         dumps = dumps_fn or self.serializer.dumps
 
@@ -82,6 +82,28 @@ async def multi_set(self, pairs, dumps_fn=None):
                     (self._build_key(key), dumps(value)) for key, value in pairs))
             return await redis.mset(*serialized_pairs)
 
+    async def add(self, key, value, ttl=None, dumps_fn=None):
+        """
+        Stores the value in the given key with ttl if specified. Raises an error if the
+        key already exists.
+
+        :param key: str
+        :param value: obj
+        :param ttl: int the expiration time in seconds
+        :param dumps_fn: callable alternative to use as dumps function
+        :returns: True if key is inserted
+        :raises: Value error if key already exists
+        """
+        dumps = dumps_fn or self.serializer.dumps
+        ttl = ttl or 0
+
+        key = self._build_key(key)
+        with await self._connect() as redis:
+            if await redis.exists(key):
+                raise ValueError(
+                    "Key {} already exists, use .set to update the value".format(key))
+            return await redis.set(key, dumps(value), expire=ttl)
+
     async def delete(self, key):
         """
         Deletes the given key.

tests/test_base_backends.py

@@ -148,3 +148,13 @@ async def test_get_set_alt_serializer_class(self, cache):
         cache.serializer = my_serializer
         await cache.set(pytest.KEY, my_obj)
         assert await cache.get(pytest.KEY) == my_serializer.loads(my_serializer.dumps(my_obj))
+
+    @pytest.mark.asyncio
+    async def test_add_missing(self, cache):
+        assert await cache.add(pytest.KEY, "value") is True
+
+    @pytest.mark.asyncio
+    async def test_add_existing(self, cache):
+        await cache.set(pytest.KEY, "value") is True
+        with pytest.raises(ValueError):
+            await cache.add(pytest.KEY, "value")