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Created October 27, 2011 18:13
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Memcached Property Attributes
"""
Property attributes in memcached
:copyright: (c) 2011 by Ori Livneh
:license: Public Domain
"""
from django.core.cache import cache
def memcached_property(key_function, timeout=cache.default_timeout, doc=None):
"""
Creates a property attribute that is stored in memcached. `key_function`
should be a callable that accepts an object instance and returns a string
representing a memcached key. Example::
class Book(models.Model):
isbn = models.CharField(max_length=13, primary_key=True)
last_read = memcached_property(
lambda self: "book:%d:last_read" % self.isbn)
:param key_function: a callable that accepts an object instance and returns
a string representing a memcached key.
:param timeout: used by setter to specify expiry; defaults to Django
default.
:param doc: If given, doc will be the docstring of the property attribute.
"""
if doc is None:
doc = memcached_property.__doc__
def fget(self):
""" Getter function """
key = key_function(self)
return cache.get(key)
def fset(self, value):
""" Setter function """
key = key_function(self)
cache.set(key, value, timeout)
def fdel(self):
""" Deleter function """
key = key_function(self)
cache.delete(key)
return property(fget, fset, fdel, doc)
if __name__ == '__main__':
# when invoked as a script, run unit test
import unittest
from datetime import datetime, timedelta
class Book(object):
""" Dummy class for testing memcached_property """
def __init__(self, isbn):
self.isbn = isbn
last_read = memcached_property(lambda b: "book:%d:last_read" % b.isbn)
class MemcachedPropertyTestCase(unittest.TestCase):
""" Test case for memcached_property descriptor """
def setUp(self):
""" Delete leftover keys in memcache """
cache.delete("book:12:last_read")
tearDown = setUp
def test_descriptor_access(self):
"""
Tests getter, setter and deleter functions for memcached properties
"""
book = Book(isbn=12)
# test init
self.assertIsNone(book.last_read)
# test setter
date = datetime.now()
book.last_read = date
self.assertEqual(book.last_read, date)
self.assertEqual(cache.get("book:12:last_read"), date)
# test that the getter function really does go to memcached by
# changing the value in memcached directly.
different_date = date - timedelta(hours=1)
self.assertNotEqual(date, different_date)
cache.set("book:12:last_read", different_date)
self.assertEqual(book.last_read, different_date)
# test the deleter function
del book.last_read
self.assertIsNone(book.last_read)
# cache.add should return true if the key did not exist, thereby
# conforming deletion.
self.assertTrue(cache.add("book:12:last_read", 123))
unittest.main()
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