db.py 文件源码

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)))