Rex, My appologies. Though the feature is in 1.0 I gave a link to the 1.1 documentation.
Django 1.0 docs: http://docs.djangoproject.com/en/1.0/topics/db/models/#id7 2009/6/3 Ian Lewis <ianmle...@gmail.com> > 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/ > ======================================= > -- ======================================= 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 -~----------~----~----~----~------~----~------~--~---
