Hi Malcolm and others, Malcolm Tredinnick schrieb: > On Wed, 2009-08-12 at 11:39 +0200, Thomas Guettler wrote: >> Hi, >> >> I am writing a workflow engine. The base workflow is stored in the DB. >> But some code needs to written for most workflows. >> >> This means I need code for a model instance (and not code per mode class). >> >> To make this most pythonic, how could this be done? >> >> My idea: since I want the workflow to be portable to several installations, >> I don't use >> serial IDs for primary keys, but slug-fields. The slug-field could be a >> importable >> classname like 'foo.workflow.MyClass'. > > You already have the content type table for referring to other model > objects. Why not use that so that you can maintain some referential > integrity?
Content Types use serial keys. Take something like a ticket system: Serial keys are good for the tickets. But if you have something like a TicketTypeModel it is not a good solution. The customer uses the live system and can create new TicketTypes. But during the same time, I might create new TicketTypes in my development system. The serial IDs clash. And the TicketTypes or (Workflow-Models) need to be installable for several customers. >> Now I want that the Workflow model instance inherits from MyClass. This must >> be done at runtime. I think this could be done with a custom manager. > > This is where I become Old Conservative Malcolm and say that you might > want to consider NOT abusing model inheritance! :) I have reasons, > though, so let me explain... ... thank you for this hint. Up to now, I don't need model inheritance at runtime. The model instance would inherit from a normal python class. I even did not think about it. But you did and that's good. I drop my first idea, because I understand, that doing model inheritance at runtime does smell bad. > > I try to always relate this back to Python and what you can do in Python > with normal classes (Django's ORM just provides a way to store parts of > classes on disk). You can do what you want in Python, using the type() > command where you can create whatever base classes you like. .... Yes, I have your opinion, too. Thomas Güttler -- Thomas Guettler, http://www.thomas-guettler.de/ E-Mail: guettli (*) thomas-guettler + de --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to [email protected] 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 -~----------~----~----~----~------~----~------~--~---
