On Tue, 2007-04-17 at 09:09 -0700, Vinay Sajip wrote: > Malcolm is right when he's talking about validation of user-entered > data. However, invariants are also used to catch programming errors; > it's certainly possible to have buggy business logic code which causes > invariant checks to fail. An alternative to overriding the save() > method is to hook the pre_save event and call a model-class invariant > method to check if, from the model point of view, the model instance > is valid. (Note that the model point of view can be stricter and also > more complex than database constraints can easily capture.) If the > invariant fails, an exception can be thrown, and caught in the view to > display an appropriate user-friendly message.
Vinay, Thanks very much. I was browsing through the Validator code, but wasn't aware of the pre_save hook. That sounds like the right place to put these kinds of checks. I've always been taught to design with class invariants explicitly defined and checked (when not detrimental to performance). Definitely a practice I'd recommend, and putting it in a centralized place like this (rather than in every view that might touch the object) is consistent with the DRY principle. Mike --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
