"Database cache backend."
import base64
import pickle
from datetime import datetime, timezone
from django.conf import settings
from django.core.cache.backends.base import DEFAULT_TIMEOUT, BaseCache
from django.db import DatabaseError, connections, models, router, transaction
from django.utils.timezone import now as tz_now
class Options:
"""A class that will quack like a Django model _meta class.
This allows cache operations to be controlled by the router
"""
def __init__(self, table):
self.db_table = table
self.app_label = "django_cache"
self.model_name = "cacheentry"
self.verbose_name = "cache entry"
self.verbose_name_plural = "cache entries"
self.object_name = "CacheEntry"
self.abstract = False
self.managed = True
self.proxy = False
self.swapped = False
class BaseDatabaseCache(BaseCache):
def __init__(self, table, params):
super().__init__(params)
self._table = table
class CacheEntry:
_meta = Options(table)
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 and whether the database supports time zones. The ORM's
# conversion and adaptation infrastructure is then used to avoid comparing
# aware and naive datetimes accidentally.
pickle_protocol = pickle.HIGHEST_PROTOCOL
def get(self, key, default=None, version=None):
return self.get_many([key], version).get(key, default)
def get_many(self, keys, version=None):
if not keys:
return {}
key_map = {
self.make_and_validate_key(key, version=version): key for key in keys
}
db = router.db_for_read(self.cache_model_class)
connection = connections[db]
quote_name = connection.ops.quote_name
table = quote_name(self._table)
with connection.cursor() as cursor:
cursor.execute(
"SELECT %s, %s, %s FROM %s WHERE %s IN (%s)"
% (
quote_name("cache_key"),
quote_name("value"),
quote_name("expires"),
table,
quote_name("cache_key"),
", ".join(["%s"] * len(key_map)),
),
list(key_map),
)
rows = cursor.fetchall()
result = {}
expired_keys = []
expression = models.Expression(output_field=models.DateTimeField())
converters = connection.ops.get_db_converters(
expression
) + expression.get_db_converters(connection)
for key, value, expires in rows:
for converter in converters:
expires = converter(expires, expression, connection)
if expires < tz_now():
expired_keys.append(key)
else:
value = connection.ops.process_clob(value)
value = pickle.loads(base64.b64decode(value.encode()))
result[key_map.get(key)] = value
self._base_delete_many(expired_keys)
return result
def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
key = self.make_and_validate_key(key, version=version)
self._base_set("set", key, value, timeout)
def add(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
key = self.make_and_validate_key(key, version=version)
return self._base_set("add", key, value, timeout)
def touch(self, key, timeout=DEFAULT_TIMEOUT, version=None):
key = self.make_and_validate_key(key, version=version)
return self._base_set("touch", key, None, timeout)
def _base_set(self, mode, key, value, timeout=DEFAULT_TIMEOUT):
timeout = self.get_backend_timeout(timeout)
db = router.db_for_write(self.cache_model_class)
connection = connections[db]
quote_name = connection.ops.quote_name
table = quote_name(self._table)
with connection.cursor() as cursor:
cursor.execute("SELECT COUNT(*) FROM %s" % table)
num = cursor.fetchone()[0]
now = tz_now()
now = now.replace(microsecond=0)
if timeout is None:
exp = datetime.max
else:
tz = timezone.utc if settings.USE_TZ else None
exp = datetime.fromtimestamp(timeout, tz=tz)
exp = exp.replace(microsecond=0)
if num > self._max_entries:
self._cull(db, cursor, now, num)
pickled = pickle.dumps(value, self.pickle_protocol)
# The DB column is expecting a string, so make sure the value is a
# string, not bytes. Refs #19274.
b64encoded = base64.b64encode(pickled).decode("latin1")
try:
# Note: typecasting for datetimes is needed by some 3rd party
# database backends. All core backends work without typecasting,
# so be careful about changes here - test suite will NOT pick
# regressions.
with transaction.atomic(using=db):
cursor.execute(
"SELECT %s, %s FROM %s WHERE %s = %%s"
% (
quote_name("cache_key"),
quote_name("expires"),
table,
quote_name("cache_key"),
),
[key],
)
result = cursor.fetchone()
if result:
current_expires = result[1]
expression = models.Expression(
output_field=models.DateTimeField()
)
for converter in connection.ops.get_db_converters(
expression
) + expression.get_db_converters(connection):
current_expires = converter(
current_expires, expression, connection
)
exp = connection.ops.adapt_datetimefield_value(exp)
if result and mode == "touch":
cursor.execute(
"UPDATE %s SET %s = %%s WHERE %s = %%s"
% (table, quote_name("expires"), quote_name("cache_key")),
[exp, key],
)
elif result and (
mode == "set" or (mode == "add" and current_expires < now)
):
cursor.execute(
"UPDATE %s SET %s = %%s, %s = %%s WHERE %s = %%s"
% (
table,
quote_name("value"),
quote_name("expires"),
quote_name("cache_key"),
),
[b64encoded, exp, key],
)
elif mode != "touch":
cursor.execute(
"INSERT INTO %s (%s, %s, %s) VALUES (%%s, %%s, %%s)"
% (
table,
quote_name("cache_key"),
quote_name("value"),
quote_name("expires"),
),
[key, b64encoded, exp],
)
else:
return False # touch failed.
except DatabaseError:
# To be threadsafe, updates/inserts are allowed to fail silently
return False
else:
return True
def delete(self, key, version=None):
key = self.make_and_validate_key(key, version=version)
return self._base_delete_many([key])
def delete_many(self, keys, version=None):
keys = [self.make_and_validate_key(key, version=version) for key in keys]
self._base_delete_many(keys)
def _base_delete_many(self, keys):
if not keys:
return False
db = router.db_for_write(self.cache_model_class)
connection = connections[db]
quote_name = connection.ops.quote_name
table = quote_name(self._table)
with connection.cursor() as cursor:
cursor.execute(
"DELETE FROM %s WHERE %s IN (%s)"
% (
table,
quote_name("cache_key"),
", ".join(["%s"] * len(keys)),
),
keys,
)
return bool(cursor.rowcount)
def has_key(self, key, version=None):
key = self.make_and_validate_key(key, version=version)
db = router.db_for_read(self.cache_model_class)
connection = connections[db]
quote_name = connection.ops.quote_name
now = tz_now().replace(microsecond=0, tzinfo=None)
with connection.cursor() as cursor:
cursor.execute(
"SELECT %s FROM %s WHERE %s = %%s and %s > %%s"
% (
quote_name("cache_key"),
quote_name(self._table),
quote_name("cache_key"),
quote_name("expires"),
),
[key, connection.ops.adapt_datetimefield_value(now)],
)
return cursor.fetchone() is not None
def _cull(self, db, cursor, now, num):
if self._cull_frequency == 0:
self.clear()
else:
connection = connections[db]
table = connection.ops.quote_name(self._table)
cursor.execute(
"DELETE FROM %s WHERE %s < %%s"
% (
table,
connection.ops.quote_name("expires"),
),
[connection.ops.adapt_datetimefield_value(now)],
)
deleted_count = cursor.rowcount
remaining_num = num - deleted_count
if remaining_num > self._max_entries:
cull_num = remaining_num // self._cull_frequency
cursor.execute(
connection.ops.cache_key_culling_sql() % table, [cull_num]
)
last_cache_key = cursor.fetchone()
if last_cache_key:
cursor.execute(
"DELETE FROM %s WHERE %s < %%s"
% (
table,
connection.ops.quote_name("cache_key"),
),
[last_cache_key[0]],
)
def clear(self):
db = router.db_for_write(self.cache_model_class)
connection = connections[db]
table = connection.ops.quote_name(self._table)
with connection.cursor() as cursor:
cursor.execute("DELETE FROM %s" % table)