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Fixed #4831 -- Added an "add" cache key method, for parity with memca…

…ched's

API. This works for all cache backends. Patch from Matt McClanahan.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@6572 bcc190cf-cafb-0310-a4f2-bffc1f526a37
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commit 714c09b8bdba069d2de49c5cf58f500497711f85 1 parent b678601
@malcolmt malcolmt authored
View
8 django/core/cache/backends/base.py
@@ -14,6 +14,14 @@ def __init__(self, params):
timeout = 300
self.default_timeout = timeout
+ def add(self, key, value, timeout=None):
+ """
+ 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.
+ """
+ raise NotImplementedError
+
def get(self, key, default=None):
"""
Fetch a given key from the cache. If the key does not exist, return
View
11 django/core/cache/backends/db.py
@@ -24,6 +24,9 @@ def __init__(self, table, params):
except (ValueError, TypeError):
self._cull_frequency = 3
+ def add(self, key, value, timeout=None):
+ return self._base_set('add', key, value, timeout)
+
def get(self, key, default=None):
cursor = connection.cursor()
cursor.execute("SELECT cache_key, value, expires FROM %s WHERE cache_key = %%s" % self._table, [key])
@@ -38,6 +41,9 @@ def get(self, key, default=None):
return pickle.loads(base64.decodestring(row[1]))
def set(self, key, value, timeout=None):
+ return self._base_set('set', key, value, timeout)
+
+ def _base_set(self, mode, key, value, timeout=None):
if timeout is None:
timeout = self.default_timeout
cursor = connection.cursor()
@@ -50,10 +56,11 @@ def set(self, key, value, timeout=None):
encoded = base64.encodestring(pickle.dumps(value, 2)).strip()
cursor.execute("SELECT cache_key FROM %s WHERE cache_key = %%s" % self._table, [key])
try:
- if cursor.fetchone():
+ if mode == 'set' and cursor.fetchone():
cursor.execute("UPDATE %s SET value = %%s, expires = %%s WHERE cache_key = %%s" % self._table, [encoded, str(exp), key])
else:
- cursor.execute("INSERT INTO %s (cache_key, value, expires) VALUES (%%s, %%s, %%s)" % self._table, [key, encoded, str(exp)])
+ if mode == 'add':
+ 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
View
3  django/core/cache/backends/dummy.py
@@ -6,6 +6,9 @@ class CacheClass(BaseCache):
def __init__(self, *args, **kwargs):
pass
+ def add(self, *args, **kwargs):
+ pass
+
def get(self, key, default=None):
return default
View
20 django/core/cache/backends/filebased.py
@@ -17,6 +17,26 @@ def __init__(self, dir, params):
del self._cache
del self._expire_info
+ def add(self, key, value, timeout=None):
+ fname = self._key_to_file(key)
+ if timeout is None:
+ timeout = self.default_timeout
+ try:
+ filelist = os.listdir(self._dir)
+ except (IOError, OSError):
+ self._createdir()
+ filelist = []
+ if len(filelist) > self._max_entries:
+ self._cull(filelist)
+ if os.path.basename(fname) not in filelist:
+ try:
+ f = open(fname, 'wb')
+ now = time.time()
+ pickle.dump(now + timeout, f, 2)
+ pickle.dump(value, f, 2)
+ except (IOError, OSError):
+ pass
+
def get(self, key, default=None):
fname = self._key_to_file(key)
try:
View
7 django/core/cache/backends/locmem.py
@@ -14,6 +14,13 @@ def __init__(self, host, params):
SimpleCacheClass.__init__(self, host, params)
self._lock = RWLock()
+ def add(self, key, value, timeout=None):
+ self._lock.writer_enters()
+ try:
+ SimpleCacheClass.add(self, key, value, timeout)
+ finally:
+ self._lock.writer_leaves()
+
def get(self, key, default=None):
should_delete = False
self._lock.reader_enters()
View
3  django/core/cache/backends/memcached.py
@@ -16,6 +16,9 @@ def __init__(self, server, params):
BaseCache.__init__(self, params)
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)
+
def get(self, key, default=None):
val = self._cache.get(smart_str(key))
if val is None:
View
9 django/core/cache/backends/simple.py
@@ -21,6 +21,15 @@ def __init__(self, host, params):
except (ValueError, TypeError):
self._cull_frequency = 3
+ def add(self, key, value, timeout=None):
+ if len(self._cache) >= self._max_entries:
+ self._cull()
+ if timeout is None:
+ timeout = self.default_timeout
+ if key not in self._cache.keys():
+ self._cache[key] = value
+ self._expire_info[key] = time.time() + timeout
+
def get(self, key, default=None):
now = time.time()
exp = self._expire_info.get(key)
View
9 docs/cache.txt
@@ -326,6 +326,15 @@ get() can take a ``default`` argument::
>>> cache.get('my_key', 'has expired')
'has expired'
+To add a key only if it doesn't already exist, there is an add() method. It
+takes the same parameters as set(), but will not attempt to update the cache
+if the key specified is already present::
+
+ >>> cache.set('add_key', 'Initial value')
+ >>> cache.add('add_key', 'New value')
+ >>> 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)::
View
6 tests/regressiontests/cache/tests.py
@@ -19,6 +19,12 @@ def test_simple(self):
cache.set("key", "value")
self.assertEqual(cache.get("key"), "value")
+ def test_add(self):
+ # test add (only add if key isn't already in cache)
+ cache.add("addkey1", "value")
+ cache.add("addkey1", "newvalue")
+ self.assertEqual(cache.get("addkey1"), "value")
+
def test_non_existent(self):
# get with non-existent keys
self.assertEqual(cache.get("does_not_exist"), None)
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