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)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.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

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))