Rex, Django parent model instances will also have a property equal to the lowercase name of the subclass. So for Animal instances that happen to be a Duck you can do something like "my_room.animal.duck" to get the Duck instance. Depending on what you are doing you might want to try that. It's reasonable enough if you are dealing with a small number of instances.
See: http://docs.djangoproject.com/en/dev/topics/db/models/#multi-table-inheritance Ian On Mon, Jun 1, 2009 at 3:49 PM, Daniel Roseman < roseman.dan...@googlemail.com> wrote: > > On Jun 1, 5:39 am, Rex <rex.eastbou...@gmail.com> wrote: > > Hello, > > > > I have a question that is best illustrated by the following fictional > > example. (I put my question at the end.) > > > > #========= > > # In models.py > > class Room(models.Model): > > animal = models.ForeignKey(Animal) > > > > class Animal(models.Model): > > #[...] > > > > class Duck(Animal): > > #[...] > > > > # In views.py > > my_duck = Duck() > > #[...] > > > > my_room = Room(animal=my_duck) > > #[...] > > > > # QUESTION: What should the following expression return? > > isinstance(my_room.animal, Duck) > > #========= > > > > Django appears to return False. Accordingly, I get an error when I try > > to call the quack() method on my_room.animal, since that method is > > defined for Ducks but not for Animals. I am running into a situation > > where I would like to call the quack() method if the room's animal is > > an instance of Duck. Is there some way to do this? > > > > Regards, > > > > Rex > > This is a reasonably frequently asked question. > > As the documentation points out, if you ask Django for an instance of > the parent class, that's what you'll get. There's no way to get from > that to the derived class, as the database doesn't record that > information. So the best thing to do is to have an 'animal_type' field > on your parent class, which is set automatically on save to whatever > type the child class is - then you could have a method on the parent > class which returns the actual object. > -- > DR. > > > -- ======================================= 株式会社ビープラウド イアン・ルイス 〒150-0012 東京都渋谷区広尾1-11-2アイオス広尾ビル604 email: ianmle...@beproud.jp TEL：03-5795-2707 FAX：03-5795-2708 http://www.beproud.jp/ ======================================= --~--~---------~--~----~------------~-------~--~----~ 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 django-users+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
