"Database cache backend." import base64 import pickle 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, models, router, transaction from django.utils import timezone from django.utils.inspect import func_supports_parameter 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 = {} for key in keys: self.validate_key(key) key_map[self.make_key(key, version)] = key 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: if func_supports_parameter(converter, 'context'): # RemovedInDjango30Warning expires = converter(expires, expression, connection, {}) else: expires = converter(expires, expression, connection) if expires < timezone.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_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 touch(self, key, timeout=DEFAULT_TIMEOUT, version=None): key = self.make_key(key, version=version) self.validate_key(key) 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 = 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, 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)): if func_supports_parameter(converter, 'context'): # RemovedInDjango30Warning current_expires = converter(current_expires, expression, connection, {}) else: 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): self.delete_many([key], version) def delete_many(self, keys, version=None): key_list = [] for key in keys: self.validate_key(key) key_list.append(self.make_key(key, version)) self._base_delete_many(key_list) def _base_delete_many(self, keys): if not keys: return 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, ) 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) connection = connections[db] quote_name = connection.ops.quote_name if settings.USE_TZ: now = datetime.utcnow() else: now = datetime.now() now = now.replace(microsecond=0) with connection.cursor() as cursor: cursor.execute( 'SELECT %s FROM %s WHERE %s = %%s and expires > %%s' % ( quote_name('cache_key'), quote_name(self._table), quote_name('cache_key'), ), [key, connection.ops.adapt_datetimefield_value(now)] ) return cursor.fetchone() is not None def _cull(self, db, cursor, now): if self._cull_frequency == 0: self.clear() else: connection = connections[db] table = connection.ops.quote_name(self._table) cursor.execute("DELETE FROM %s WHERE expires < %%s" % table, [connection.ops.adapt_datetimefield_value(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( connection.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) connection = connections[db] table = connection.ops.quote_name(self._table) with connection.cursor() as cursor: cursor.execute('DELETE FROM %s' % table)