On Fri, 2008-09-12 at 11:57 -0700, dadapapa wrote: > > It does not work at all. For some reason, final_type also gets > > upcasted to MediaObject?! > > I found the solution, now. The problem was that the __init__ method of > a Model is also called when objects are restored from the database. So > when the base class gets initialized by the QueryManager, it > overwrites final_type with the wrong value. The solution is simple: > overwrite the save method instead of __init__. Here is a complete > recipe: > > class BaseClass(models.Model) : > final_type = models.ForeignKey(ContentType) > > def save(self,*args) :
For absolute robustness, you should also accept **kwargs here. There are a couple of places in Django's code that will call save() and pass in force_insert=True, for example, which won't be handled by *args. In reality, all you need to be able to handle is force_insert and force_update, but *args and **kwargs are also pretty useful, particularly if you aren't doing anything with them except passing them along. > self.final_type = > ContentType.objects.get_for_model(type(self)) > super(BaseClass,self)save(*args) > > def cast(self) : > return > self.final_type.get_object_for_this_type(id=self.id) > > class DerivedClass(ParentClass) : > pass > > Here is an example: > > obj = DerivedClass() > obj.save() > > obj = get_object_or_404(BaseClass, id=3).cast() > # obj is now of type DerivedClass Yes, well done. This looks like the right way to handle this. Glad somebody's documented it here. Regards, Malcolm --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
