Though I'm not sure what MTI is (Google suggest "Massage Training Institute", but that can't be right), what you're trying to do seems well within Django's capabilities.
Generic relations allow you to create foreign keys to any other object, so you'd have a Generic Foreign Key in your enclosure, then that could contain any kind of animal (or tree, car or building for that matter). Have another look here: http://www.djangoproject.com/documentation/models/generic_relations/, it's so close to what you're doing that I think you can steal most of the code you need. Alll the best, Kip On Aug 21, 6:40 am, Shay <[EMAIL PROTECTED]> wrote: > Hi, > > Thanks for the tip, I found Generic Relations and GenericForeignKey > shortly after I posted this and you confirmed I was looking in the > right place. :) > > It seemed a better idea to make Animalabstractsince I don't want it > to be able to be instantiated on its own. ZooEnclosure should only be > able to accept anything that is a type of Animal but not Animal itself > since it contains no valuable information in isolation of its > subclasses. Is there a way of preventing this without making the > classabstract? > > Also are there any scalability issues with using MTI for this type of > design (Particularly on large tables)? > > With respect to implementing that design as a generic relation (sort > of based onhttp://www.djangoproject.com/documentation/contenttypes/ > andhttp://www.webmonkey.com/tutorial/Build_a_Microblog_with_Django), > I'm still a little fuzzy on this, but would the implementation be > something to the effect of: > > class Animal(models.Model): > content_type = models.ForeignKey(ContentType) > object_id = models.PositiveIntegerField() > content_object = generic.GenericForeignKey('content_type', > 'object_id') > ... > > class Meta: > abstract= True > > class Zebra(Animal): > /* Inherits the content_type, object_id, content_object attributes > from Animal */ > ... > > class Snake(Animal): > ... > > class ZooEnclosure(models.Model): > enclosureName = models.CharField(max_length=50) > > And then when ZooEnclosure is instantiated (form or otherwise), > there's either hook or some signal event which will trigger the > creation of the instance of Animal. > > Am I on the right track or completely off? > > Also since ZooEnclosure could contain any type of animal, I can't > recreate a reverse GenericRelation here for inhabitedBy. Creating a > GenericRelation to Animal would, I'm guessing, leave me with the same > problem as before because I set it asabstract(and the same other > problem of unflattened table hierarchy if I didn't set it asabstract). Is it > possible to specify this in the model? > > If these are elementary questions, my apologies, I'm still trying to > get my head around how all of this hangs together. :) > > Thanks, > Shay > > On Aug 20, 5:21 pm, Kip Parker <[EMAIL PROTECTED]> wrote: > > > Maybe have a look at generic > > relations?http://www.djangoproject.com/documentation/models/generic_relations/ > > > You could also use multi-table inheritance rather thanabstract > > classes, then use the parent class Animal as the key in ZooEnclosure. > >Abstractclasses can't exist on their own, which I expect is why you > > got the NoneType errors. > > > Kip. > > > On Aug 20, 3:57 am, Shay <[EMAIL PROTECTED]> wrote: > > > > Hi, > > > > I'm rather new to Django, so please bear with me. :P > > > > I've been trying to figure out how to implement the following in > > > models: > > > > class: Animal (abstractclass) > > > ... > > > > class: Zebra (extends Animal) > > > ... > > > > class: Snake (extends Animal) > > > ... > > > > class: ZooEnclosure > > > String enclosureName > > > Animal inhabitedBy > > > > So: > > > - This is a very trivial example > > > - Zebra and Snake are subclasses of theabstractclass Animal > > > - ZooEnclosure is composed of some sort of Animal where I could > > > feasibly use a Zebra or a Snake > > > > Creating a new ZooEnclosure for every animal is not an option because > > > there're quite a few and could quite possibly result in a hundred > > > different classes just to change the animal. > > > > I've looked at the MTI and ABC type documentation (and Google) but I'm > > > still not clear on how best to implement this in Django Models. > > > > Oh and when I have attempted to leave Animalabstract, it gives me > > > NoneType errors. > > > > I'm not sure what the best way to tackle this problem is, any > > > suggestions? --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
