[Zope] Setting attribute from DTML method in ZClass

Hi, I've created a ZClass with a method 'force_update'. When a user is viewing an object, there is a formbutton which they can press and force_update is then called. So far it works. What I want my force_update to do, is that it should set the needs_check (type boolean) in the object to true. With <dtml-if needs_check> I print different things depending on whether the object needs a check. From the Property sheet I can change the settings. So, how do I put something like this().needs_check = 1 in a dtml-method? Greetings, Chris Niekel