Fixed #14596 -- Light refactoring of the cache backends.

* Removes some code duplication,
 * Provides a convenient base class for db-like cache backends
 * Adds tests for an edge case of culling,
 * Marks the memcached tests as "skipped", rather than omitting them.

Thanks to Jonas H for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14434 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/core/cache/backends/base.py

@@ -22,6 +22,18 @@ class BaseCache(object):
             timeout = 300
         self.default_timeout = timeout
 
+        max_entries = params.get('max_entries', 300)
+        try:
+            self._max_entries = int(max_entries)
+        except (ValueError, TypeError):
+            self._max_entries = 300
+
+        cull_frequency = params.get('cull_frequency', 3)
+        try:
+            self._cull_frequency = int(cull_frequency)
+        except (ValueError, TypeError):
+            self._cull_frequency = 3
+
     def add(self, key, value, timeout=None):
         """
         Set a value in the cache if the key does not already exist. If

django/core/cache/backends/db.py

@@ -25,7 +25,7 @@ class Options(object):
         self.managed = True
         self.proxy = False
 
-class CacheClass(BaseCache):
+class BaseDatabaseCacheClass(BaseCache):
     def __init__(self, table, params):
         BaseCache.__init__(self, params)
         self._table = table
@@ -34,17 +34,7 @@ class CacheClass(BaseCache):
             _meta = Options(table)
         self.cache_model_class = CacheEntry
 
-        max_entries = params.get('max_entries', 300)
+class CacheClass(BaseDatabaseCacheClass):
-        try:
-            self._max_entries = int(max_entries)
-        except (ValueError, TypeError):
-            self._max_entries = 300
-        cull_frequency = params.get('cull_frequency', 3)
-        try:
-            self._cull_frequency = int(cull_frequency)
-        except (ValueError, TypeError):
-            self._cull_frequency = 3
-
     def get(self, key, default=None):
         self.validate_key(key)
         db = router.db_for_read(self.cache_model_class)

django/core/cache/backends/filebased.py

@@ -14,19 +14,6 @@ from django.utils.hashcompat import md5_constructor
 class CacheClass(BaseCache):
     def __init__(self, dir, params):
         BaseCache.__init__(self, params)
-
-        max_entries = params.get('max_entries', 300)
-        try:
-            self._max_entries = int(max_entries)
-        except (ValueError, TypeError):
-            self._max_entries = 300
-
-        cull_frequency = params.get('cull_frequency', 3)
-        try:
-            self._cull_frequency = int(cull_frequency)
-        except (ValueError, TypeError):
-            self._cull_frequency = 3
-
         self._dir = dir
         if not os.path.exists(self._dir):
             self._createdir()

django/core/cache/backends/locmem.py

@@ -14,19 +14,6 @@ class CacheClass(BaseCache):
         BaseCache.__init__(self, params)
         self._cache = {}
         self._expire_info = {}
-
-        max_entries = params.get('max_entries', 300)
-        try:
-            self._max_entries = int(max_entries)
-        except (ValueError, TypeError):
-            self._max_entries = 300
-
-        cull_frequency = params.get('cull_frequency', 3)
-        try:
-            self._cull_frequency = int(cull_frequency)
-        except (ValueError, TypeError):
-            self._cull_frequency = 3
-
         self._lock = RWLock()
 
     def add(self, key, value, timeout=None):

tests/regressiontests/cache/tests.py

@@ -410,6 +410,10 @@ class DBCacheTests(unittest.TestCase, BaseCacheTests):
     def test_cull(self):
         self.perform_cull_test(50, 29)
 
+    def test_zero_cull(self):
+        self.cache = get_cache('db://%s?max_entries=30&cull_frequency=0' % self._table_name)
+        self.perform_cull_test(50, 18)
+
 class LocMemCacheTests(unittest.TestCase, BaseCacheTests):
     def setUp(self):
         self.cache = get_cache('locmem://?max_entries=30')
@@ -417,12 +421,15 @@ class LocMemCacheTests(unittest.TestCase, BaseCacheTests):
     def test_cull(self):
         self.perform_cull_test(50, 29)
 
+    def test_zero_cull(self):
+        self.cache = get_cache('locmem://?max_entries=30&cull_frequency=0')
+        self.perform_cull_test(50, 19)
+
 # memcached backend isn't guaranteed to be available.
 # To check the memcached backend, the test settings file will
 # need to contain a CACHE_BACKEND setting that points at
 # your memcache server.
-if settings.CACHE_BACKEND.startswith('memcached://'):
+class MemcachedCacheTests(unittest.TestCase, BaseCacheTests):
-    class MemcachedCacheTests(unittest.TestCase, BaseCacheTests):
     def setUp(self):
         self.cache = get_cache(settings.CACHE_BACKEND)
 
@@ -440,7 +447,7 @@ if settings.CACHE_BACKEND.startswith('memcached://'):
         self.assertRaises(Exception, self.cache.set, 'key with spaces', 'value')
         # memcached limits key length to 250
         self.assertRaises(Exception, self.cache.set, 'a' * 251, 'value')
-
+MemcachedCacheTests = unittest.skipUnless(settings.CACHE_BACKEND.startswith('memcached://'), "memcached not available")(MemcachedCacheTests)
 
 class FileBasedCacheTests(unittest.TestCase, BaseCacheTests):
     """