Hi, I often have more luck the second time I ask a question... let's see if this rule holds. I'm struggling with checking and reporting errors in forms that create or modify properties of PD classes in a ZPatterns application. Automatic checks using Zope's built-in constraints or something like ValueHandler won't cut it, because they can't cover all the required rules - for example, checking if a Product SKU is being set to an existing SKU, or that a Customer is trying to use an email address already in use (and also because I want to return the form page with the errors indicated, rather than a generic error page). So I need a specific verification method for each class. This method will be used both when an object is edited and when its created. To use the method when creating an object, I either have to place it in the Specialist - which is bad, because the PD class should provide its validation code, or call it at commit time, using a SkinScript WHEN OBJECT CREATED,CHANGED clause. But verification methods called at commit time do their checks on the object properties, not on any submitted form field values. So they can test that a password is reasonably secure, but can't check that passwords typed in two form fields are identical. One thing I can do is define a editInstance method which would verify the values in REQUEST.form and then call manage_changeProperties, or store a list of errors in the REQUEST and raise a 'FormError' exception. But I can't let this exception propagate freely, I have to catch it so I can display an appropriate error page. Also, if a form results in the creation of more than one object, I want to display all the errors that result from the creation of all the objects, but if the first object raises an exception, I can't create the second one (especially if the second one expects to get the id of the first). Or I could forget about exceptions and simply return an error list from editInstance. Then it would be up to the method calling editInstance to raise an exception to roll back the created objects. This is the only workable solution I got at the moment... I can get it to work, but I've chased solutions in the past that seemed good but ended up crashing... so I'd really appreciate any comments on possible flaws or problems I'm not seeing, or any other, better solutions. This is what it would look like (just an example, not showing cases where more complex stuff happens, like 2 objects being created with a single form): In Customer (DataSkin PD class): def editInstance(self, REQUEST, errors): err = self.verify(REQUEST) if err != {}: errors.update(err) else: self.manage_changeProperties(REQUEST) def editInstance_html(self, REQUEST, RESPONSE): """Action method for editInstanceForm_html""" errors = {} self.editInstance(REQUEST, errors) if errors != {}: html = self.editInstanceForm_html(self, REQUEST, errors=errors) raise 'FormError', html RESPONSE.redirect('editInstanceForm_html?message=Changes%20saved.') def verify(self, REQUEST): errors = {} if REQUEST['name'] == '': errors['name'] = 'Please provide a name' return errors In CustomerManager (Specialist): addCustomer(self, REQUEST, errors): ni = self.defaultRack.newItem() ni.editInstance(REQUEST, errors) return ni addCustomer_html(self, REQUEST, RESPONSE): """Action method for addCustomerForm_html""" errors = {} ni = self.addCustomer(REQUEST, errors) if errors != {}: html = self.addCustomerForm_html(self, REQUEST, errors=errors) raise 'FormError', html RESPONSE.redirect('manageInstances_html?message=New%20customer%20created.') And, of course, I can also have WHEN OBJECT ADDED,CHANGED CALL self.ensure_valid(), to catch anything that might get by the above checks. ensure_valid will raise its own error page, independent of the above. TIA for any help/comments Itai -- -- Itai Tavor -- "Je sautille, donc je suis." -- itai@optusnet.com.au -- - Kermit the Frog -- -- 'Supposing a tree fell down, Pooh, when we were underneath it?' -- -- 'Supposing it didn't,' said Pooh after careful thought. --