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Made the database cache backend, which bypasses the ORM, compatible with time zone support. 

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17119 bcc190cf-cafb-0310-a4f2-bffc1f526a37
This commit is contained in:
Aymeric Augustin 2011-11-20 10:17:12 +00:00
parent f6ee168919
commit 7075e93256
3 changed files with 59 additions and 18 deletions
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67
django/core/cache/backends/db.py vendored
View File

@ -8,8 +8,10 @@ try:
except ImportError:
import pickle
from django.conf import settings
from django.core.cache.backends.base import BaseCache
from django.db import connections, router, transaction, DatabaseError
from django.utils import timezone
class Options(object):
@ -38,6 +40,17 @@ class BaseDatabaseCache(BaseCache):
self.cache_model_class = CacheEntry
class DatabaseCache(BaseDatabaseCache):
# This class uses cursors provided by the database connection. This means
# it reads expiration values as aware or naive datetimes depending on the
# value of USE_TZ. They must be compared to aware or naive representations
# of "now" respectively.
# But it bypasses the ORM for write operations. As a consequence, aware
# datetimes aren't made naive for databases that don't support time zones.
# We work around this problem by always using naive datetimes when writing
# expiration values, in UTC when USE_TZ = True and in local time otherwise.
def get(self, key, default=None, version=None):
key = self.make_key(key, version=version)
self.validate_key(key)
@ -45,15 +58,17 @@ class DatabaseCache(BaseDatabaseCache):
table = connections[db].ops.quote_name(self._table)
cursor = connections[db].cursor()
cursor.execute("SELECT cache_key, value, expires FROM %s WHERE cache_key = %%s" % table, [key])
cursor.execute("SELECT cache_key, value, expires FROM %s "
"WHERE cache_key = %%s" % table, [key])
row = cursor.fetchone()
if row is None:
return default
now = datetime.now()
now = timezone.now()
if row[2] < now:
db = router.db_for_write(self.cache_model_class)
cursor = connections[db].cursor()
cursor.execute("DELETE FROM %s WHERE cache_key = %%s" % table, [key])
cursor.execute("DELETE FROM %s "
"WHERE cache_key = %%s" % table, [key])
transaction.commit_unless_managed(using=db)
return default
value = connections[db].ops.process_clob(row[1])
@ -78,20 +93,28 @@ class DatabaseCache(BaseDatabaseCache):
cursor.execute("SELECT COUNT(*) FROM %s" % table)
num = cursor.fetchone()[0]
now = datetime.now().replace(microsecond=0)
exp = datetime.fromtimestamp(time.time() + timeout).replace(microsecond=0)
now = timezone.now()
now = now.replace(microsecond=0)
if settings.USE_TZ:
exp = datetime.utcfromtimestamp(time.time() + timeout)
else:
exp = datetime.fromtimestamp(time.time() + timeout)
exp = exp.replace(microsecond=0)
if num > self._max_entries:
self._cull(db, cursor, now)
encoded = base64.encodestring(pickle.dumps(value, 2)).strip()
cursor.execute("SELECT cache_key, expires FROM %s WHERE cache_key = %%s" % table, [key])
cursor.execute("SELECT cache_key, expires FROM %s "
"WHERE cache_key = %%s" % table, [key])
try:
result = cursor.fetchone()
if result and (mode == 'set' or
(mode == 'add' and result[1] < now)):
cursor.execute("UPDATE %s SET value = %%s, expires = %%s WHERE cache_key = %%s" % table,
cursor.execute("UPDATE %s SET value = %%s, expires = %%s "
"WHERE cache_key = %%s" % table,
[encoded, connections[db].ops.value_to_db_datetime(exp), key])
else:
cursor.execute("INSERT INTO %s (cache_key, value, expires) VALUES (%%s, %%s, %%s)" % table,
cursor.execute("INSERT INTO %s (cache_key, value, expires) "
"VALUES (%%s, %%s, %%s)" % table,
[key, encoded, connections[db].ops.value_to_db_datetime(exp)])
except DatabaseError:
# To be threadsafe, updates/inserts are allowed to fail silently
@ -120,8 +143,13 @@ class DatabaseCache(BaseDatabaseCache):
table = connections[db].ops.quote_name(self._table)
cursor = connections[db].cursor()
now = datetime.now().replace(microsecond=0)
cursor.execute("SELECT cache_key FROM %s WHERE cache_key = %%s and expires > %%s" % table,
if settings.USE_TZ:
now = datetime.utcnow()
else:
now = datetime.now()
now = now.replace(microsecond=0)
cursor.execute("SELECT cache_key FROM %s "
"WHERE cache_key = %%s and expires > %%s" % table,
[key, connections[db].ops.value_to_db_datetime(now)])
return cursor.fetchone() is not None
@ -129,6 +157,8 @@ class DatabaseCache(BaseDatabaseCache):
if self._cull_frequency == 0:
self.clear()
else:
# When USE_TZ is True, 'now' will be an aware datetime in UTC.
now = now.replace(tzinfo=None)
table = connections[db].ops.quote_name(self._table)
cursor.execute("DELETE FROM %s WHERE expires < %%s" % table,
[connections[db].ops.value_to_db_datetime(now)])
@ -137,12 +167,19 @@ class DatabaseCache(BaseDatabaseCache):
if num > self._max_entries:
cull_num = num / self._cull_frequency
if connections[db].vendor == 'oracle':
# Special case for Oracle because it doesn't support LIMIT + OFFSET
cursor.execute("SELECT cache_key FROM (SELECT ROW_NUMBER() OVER (ORDER BY cache_key) AS counter, cache_key FROM %s) WHERE counter > %%s AND COUNTER <= %%s" % table, [cull_num, cull_num + 1])
# Oracle doesn't support LIMIT + OFFSET
cursor.execute("""SELECT cache_key FROM
(SELECT ROW_NUMBER() OVER (ORDER BY cache_key) AS counter, cache_key FROM %s)
WHERE counter > %%s AND COUNTER <= %%s""" % table, [cull_num, cull_num + 1])
else:
# This isn't standard SQL, it's likely to break with some non officially supported databases
cursor.execute("SELECT cache_key FROM %s ORDER BY cache_key LIMIT 1 OFFSET %%s" % table, [cull_num])
cursor.execute("DELETE FROM %s WHERE cache_key < %%s" % table, [cursor.fetchone()[0]])
# This isn't standard SQL, it's likely to break
# with some non officially supported databases
cursor.execute("SELECT cache_key FROM %s "
"ORDER BY cache_key "
"LIMIT 1 OFFSET %%s" % table, [cull_num])
cursor.execute("DELETE FROM %s "
"WHERE cache_key < %%s" % table,
[cursor.fetchone()[0]])
def clear(self):
db = router.db_for_write(self.cache_model_class)

4
tests/regressiontests/cache/models.py vendored
View File

@ -1,11 +1,11 @@
from datetime import datetime
from django.utils import timezone
from django.db import models
def expensive_calculation():
expensive_calculation.num_runs += 1
return datetime.now()
return timezone.now()
class Poll(models.Model):
question = models.CharField(max_length=200)

6
tests/regressiontests/cache/tests.py vendored
View File

@ -746,7 +746,7 @@ def custom_key_func(key, key_prefix, version):
return 'CUSTOM-' + '-'.join([key_prefix, str(version), key])
class DBCacheTests(unittest.TestCase, BaseCacheTests):
class DBCacheTests(BaseCacheTests, TestCase):
backend_name = 'django.core.cache.backends.db.DatabaseCache'
def setUp(self):
@ -763,6 +763,7 @@ class DBCacheTests(unittest.TestCase, BaseCacheTests):
from django.db import connection
cursor = connection.cursor()
cursor.execute('DROP TABLE %s' % connection.ops.quote_name(self._table_name))
connection.commit()
def test_cull(self):
self.perform_cull_test(50, 29)
@ -776,6 +777,9 @@ class DBCacheTests(unittest.TestCase, BaseCacheTests):
self.perform_cull_test(50, 18)
DBCacheWithTimeZoneTests = override_settings(USE_TZ=True)(DBCacheTests)
class DBCacheRouter(object):
"""A router that puts the cache table on the 'other' database."""