Added a return value to the add() method for caches. It's now possible to tell

if a call to add() ended up storing something in the cache.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8278 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/core/cache/backends/base.py

@@ -19,6 +19,8 @@ class BaseCache(object):
         Set a value in the cache if the key does not already exist. If
         timeout is given, that timeout will be used for the key; otherwise
         the default cache timeout will be used.
+
+        Returns True if the value was stored, False otherwise.
         """
         raise NotImplementedError
 

django/core/cache/backends/db.py

@@ -38,7 +38,7 @@ class CacheClass(BaseCache):
         return pickle.loads(base64.decodestring(row[1]))
 
     def set(self, key, value, timeout=None):
-        return self._base_set('set', key, value, timeout)
+        self._base_set('set', key, value, timeout)
 
     def add(self, key, value, timeout=None):
         return self._base_set('add', key, value, timeout)
@@ -62,9 +62,10 @@ class CacheClass(BaseCache):
                 cursor.execute("INSERT INTO %s (cache_key, value, expires) VALUES (%%s, %%s, %%s)" % self._table, [key, encoded, str(exp)])
         except DatabaseError:
             # To be threadsafe, updates/inserts are allowed to fail silently
-            pass
+            return False
         else:
             transaction.commit_unless_managed()
+            return True
 
     def delete(self, key):
         cursor = connection.cursor()

django/core/cache/backends/dummy.py

@@ -7,7 +7,7 @@ class CacheClass(BaseCache):
         pass
 
     def add(self, *args, **kwargs):
-        pass
+        return True
 
     def get(self, key, default=None):
         return default

django/core/cache/backends/filebased.py

@@ -32,9 +32,10 @@ class CacheClass(BaseCache):
 
     def add(self, key, value, timeout=None):
         if self.has_key(key):
-            return None
+            return False
 
         self.set(key, value, timeout)
+        return True
 
     def get(self, key, default=None):
         fname = self._key_to_file(key)

django/core/cache/backends/locmem.py

@@ -36,8 +36,10 @@ class CacheClass(BaseCache):
             if exp is None or exp <= time.time():
                 try:
                     self._set(key, pickle.dumps(value), timeout)
+                    return True
                 except pickle.PickleError:
                     pass
+            return False
         finally:
             self._lock.writer_leaves()
 

django/core/cache/backends/memcached.py

@@ -17,7 +17,7 @@ class CacheClass(BaseCache):
         self._cache = memcache.Client(server.split(';'))
 
     def add(self, key, value, timeout=0):
-        self._cache.add(key.encode('ascii', 'ignore'), value, timeout or self.default_timeout)
+        return self._cache.add(key.encode('ascii', 'ignore'), value, timeout or self.default_timeout)
 
     def get(self, key, default=None):
         val = self._cache.get(smart_str(key))

docs/cache.txt

@@ -410,9 +410,13 @@ it will not attempt to update the cache if the key specified is already present:
     >>> cache.get('add_key')
     'Initial value'
 
-There's also a ``get_many()`` interface that only hits the cache once. ``get_many()``
-returns a dictionary with all the keys you asked for that actually exist in the
-cache (and haven't expired)::
+If you need to know whether ``add()`` stored a value in the cache, you can
+check the return value. It will return ``True`` if the value was stored,
+``False`` otherwise.
+
+There's also a ``get_many()`` interface that only hits the cache once.
+``get_many()`` returns a dictionary with all the keys you asked for that
+actually exist in the cache (and haven't expired)::
 
     >>> cache.set('a', 1)
     >>> cache.set('b', 2)

tests/regressiontests/cache/tests.py

@@ -31,7 +31,8 @@ class Cache(unittest.TestCase):
     def test_add(self):
         # test add (only add if key isn't already in cache)
         cache.add("addkey1", "value")
-        cache.add("addkey1", "newvalue")
+        result = cache.add("addkey1", "newvalue")
+        self.assertEqual(result, False)
         self.assertEqual(cache.get("addkey1"), "value")
 
     def test_non_existent(self):