[Zope] Create or edit instance objects

Dear Zopeists: I guess my problem should be a classical one, but I still haven´t found a solution in any How-to or message in this list, so I have no choice to ask for your help. - HELP!!!! How can I make the same method that creates an instance object to edit it? Note: - my class uses Propertysheets - my class uses random ids. - I would like to avoid to create the instance object before all the data is set in the REQUEST (and the button "create" has been clicked) so no garbage is to be later cleaned. Lots of thanks in advance, PABLO.