"Database cache backend." import base64 from datetime import datetime from django.conf import settings from django.core.cache.backends.base import DEFAULT_TIMEOUT, BaseCache from django.db import DatabaseError, connections, router, transaction from django.db.backends.utils import typecast_timestamp from django.utils import six, timezone from django.utils.encoding import force_bytes try: from django.utils.six.moves import cPickle as pickle except ImportError: import pickle class Options(object): """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): BaseCache.__init__(self, params) self._table = table class CacheEntry(object): _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. 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) db = router.db_for_read(self.cache_model_class) table = connections[db].ops.quote_name(self._table) with connections[db].cursor() as cursor: 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 = timezone.now() expires = row[2] if connections[db].features.needs_datetime_string_cast and not isinstance(expires, datetime): # Note: typecasting 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 here. expires = typecast_timestamp(str(expires)) if expires < now: db = router.db_for_write(self.cache_model_class) with connections[db].cursor() as cursor: cursor.execute("DELETE FROM %s " "WHERE cache_key = %%s" % table, [key]) return default value = connections[db].ops.process_clob(row[1]) return pickle.loads(base64.b64decode(force_bytes(value))) def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None): key = self.make_key(key, version=version) self.validate_key(key) self._base_set('set', key, value, timeout) def add(self, key, value, timeout=DEFAULT_TIMEOUT, version=None): key = self.make_key(key, version=version) self.validate_key(key) return self._base_set('add', key, value, 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) table = connections[db].ops.quote_name(self._table) with connections[db].cursor() as cursor: cursor.execute("SELECT COUNT(*) FROM %s" % table) num = cursor.fetchone()[0] now = timezone.now() now = now.replace(microsecond=0) if timeout is None: exp = datetime.max elif settings.USE_TZ: exp = datetime.utcfromtimestamp(timeout) else: exp = datetime.fromtimestamp(timeout) exp = exp.replace(microsecond=0) if num > self._max_entries: self._cull(db, cursor, now) pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL) b64encoded = base64.b64encode(pickled) # The DB column is expecting a string, so make sure the value is a # string, not bytes. Refs #19274. if six.PY3: b64encoded = b64encoded.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 cache_key, expires FROM %s " "WHERE cache_key = %%s" % table, [key]) result = cursor.fetchone() if result: current_expires = result[1] if (connections[db].features.needs_datetime_string_cast and not isinstance(current_expires, datetime)): current_expires = typecast_timestamp(str(current_expires)) exp = connections[db].ops.value_to_db_datetime(exp) if result and (mode == 'set' or (mode == 'add' and current_expires < now)): cursor.execute("UPDATE %s SET value = %%s, expires = %%s " "WHERE cache_key = %%s" % table, [b64encoded, exp, key]) else: cursor.execute("INSERT INTO %s (cache_key, value, expires) " "VALUES (%%s, %%s, %%s)" % table, [key, b64encoded, exp]) 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_key(key, version=version) self.validate_key(key) db = router.db_for_write(self.cache_model_class) table = connections[db].ops.quote_name(self._table) with connections[db].cursor() as cursor: cursor.execute("DELETE FROM %s WHERE cache_key = %%s" % table, [key]) def has_key(self, key, version=None): key = self.make_key(key, version=version) self.validate_key(key) db = router.db_for_read(self.cache_model_class) table = connections[db].ops.quote_name(self._table) if settings.USE_TZ: now = datetime.utcnow() else: now = datetime.now() now = now.replace(microsecond=0) with connections[db].cursor() as cursor: 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 def _cull(self, db, cursor, now): 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)]) cursor.execute("SELECT COUNT(*) FROM %s" % table) num = cursor.fetchone()[0] if num > self._max_entries: cull_num = num // self._cull_frequency cursor.execute( connections[db].ops.cache_key_culling_sql() % 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) table = connections[db].ops.quote_name(self._table) with connections[db].cursor() as cursor: cursor.execute('DELETE FROM %s' % table)