Commit 638dbc3e authored by Russell Keith-Magee's avatar Russell Keith-Magee
Browse files

Fixed #6464 -- Added incr() and decr() operations on cache backends. Atomic on... 

Fixed #6464 -- Added incr() and decr() operations on cache backends. Atomic on Memcache; implemented as a 2 stage retrieve/update on other backends. Includes refactor of the cache tests to ensure all the backends are actually tested, and a fix to the DB cache backend that was discovered as a result. Thanks to Michael Malone for the original patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10031 bcc190cf-cafb-0310-a4f2-bffc1f526a37
parent 1d8e6eae

django/core/cache/backends/base.py

+18 −0
Original line number Diff line number Diff line
@@ -65,6 +65,24 @@ class BaseCache(object): 
        """

        return self.get(key) is not None



    def incr(self, key, delta=1):

        """

        Add delta to value in the cache. If the key does not exist, raise a

        ValueError exception.

        """

        if key not in self:

            raise ValueError, "Key '%s' not found" % key

        new_value = self.get(key) + delta

        self.set(key, new_value)

        return new_value



    def decr(self, key, delta=1):

        """

        Subtract delta from value in the cache. If the key does not exist, raise

        a ValueError exception.

        """

        return self.incr(key, -delta)



    def __contains__(self, key):

        """

        Returns True if the key is in the cache and has not expired.

django/core/cache/backends/db.py

+1 −0
Original line number Diff line number Diff line
@@ -64,6 +64,7 @@ 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

            transaction.rollback()

            return False

        else:

            transaction.commit_unless_managed()

django/core/cache/backends/memcached.py

+5 −0
Original line number Diff line number Diff line
@@ -45,3 +45,8 @@ class CacheClass(BaseCache): 
    def close(self, **kwargs):

        self._cache.disconnect_all()



    def incr(self, key, delta=1):

        return self._cache.incr(key, delta)



    def decr(self, key, delta=1):

        return self._cache.decr(key, delta)

docs/internals/contributing.txt

+25 −18
Original line number Diff line number Diff line
@@ -782,6 +782,10 @@ dependencies: 
    *  Textile_

    *  Docutils_

    *  setuptools_

    *  memcached_, plus the either the python-memcached_ or cmemcached_ Python binding



If you want to test the memcached cache backend, you will also need to define

a :setting:`CACHE_BACKEND` setting that points at your memcached instance.



Each of these dependencies is optional. If you're missing any of them, the

associated tests will be skipped.
@@ -791,6 +795,9 @@ associated tests will be skipped. 
.. _Textile: http://pypi.python.org/pypi/textile

.. _docutils: http://pypi.python.org/pypi/docutils/0.4

.. _setuptools: http://pypi.python.org/pypi/setuptools/

.. _memcached: http://www.danga.com/memcached/

.. _python-memcached: http://pypi.python.org/pypi/python-memcached/

.. _cmemcached: http://pypi.python.org/pypi/cmemcache



To run a subset of the unit tests, append the names of the test modules to the

``runtests.py`` command line. See the list of directories in

docs/topics/cache.txt

+28 −1
Original line number Diff line number Diff line
@@ -439,6 +439,33 @@ of clearing the cache for a particular object:: 


    >>> cache.delete('a')



.. versionadded:: 1.1



You can also increment or decrement a key that already exists using the

``incr()`` or ``decr()`` methods, respectively. By default, the existing cache

value will incremented or decremented by 1. Other increment/decrement values

can be specified by providing an argument to the increment/decrement call. A

ValueError will be raised if you attempt to increment or decrement a

nonexistent cache key.::



    >>> cache.set('num', 1)

    >>> cache.incr('num')

    2

    >>> cache.incr('num', 10)

    12

    >>> cache.decr('num')

    11

    >>> cache.decr('num', 5)

    6



.. note::



    ``incr()``/``decr()`` methods are not guaranteed to be atomic. On those

    backends that support atomic increment/decrement (most notably, the

    memcached backend), increment and decrement operations will be atomic.

    However, if the backend doesn't natively provide an increment/decrement

    operation, it will be implemented using a 2 step retrieve/update.



That's it. The cache has very few restrictions: You can cache any object that

can be pickled safely, although keys must be strings.