Question

I’ve been trying to figure this out for a while now with little success. I’m attempting to write a class factory that plays nice with Django’s ORM, so that I can take a model schema like this:

Product
    SubclassOfProduct0
    SubclassOfProduct1
    ....

To work like this:

Product.objects.get(pk=7) // returns the result of SubclassOfProduct0(pk=7)
Product.objects.filter(propname="w00t") // returns a QuerySet of Product objects

So I was thinking something like this:

class ProductManager(models.Manager):
    def get(self, *a, **kwa):
        # Get the id from Products (somehow)
        if product.type == Product.TYPE_SUBCLASS0:
            return ProductSubClass0.objects.get(pk=kwa["pk"])


class Product(models.Model):

    TYPE_SUBCLASS0 = 0
    TYPE_SUBCLASS1 = 1

    objects = ProductManager()

    def __init__(self, *a, **kwa):
        self.set_defaults()

    def set_defaults(self):
        pass


class ProductSubClass0(models.Model):
    def set_defaults(self):
        self.type == self.TYPE_SUBCLASS0

…but I don’t know how to do it “right”. Can someone shed some light here?

Answer 1

Django Tagging has a great example in the models.py as to how it figures out the content type of specific classes. I’m currently using the pattern in another module I developed with permissions.