Django multi-table inheritance, how to know which is the child class of a model?

Question

I\'m having a problem with multi-table inheritance in django.

Let’s make an example with bank accounts.

class account(models.Model):
    name = models……         


        

Answer 1

Django adds to class account two fields: accounttypea and accounttypeb. If you have accounttypeB object with pk=42, you can access from parent like this:

account.objects.get(pk=42).accounttypeb
>>> 

You can add CharField to parent model with actual child-type for every child, and then use getattr, if there are a lot of child models (it may be better than a lot of try .. except xxx.DoesNotExist blocks).

class account(models.Model):
    name = models……
    cls = CharField(...)  

    def ext(self):
        return getattr(self, self.cls.lower())


class accounttypeA(account):
    balance = models.float…..

    def addToBalance(self, value):
        self.balance += value


class accounttypeB(account):
    balance = models.int…. # NOTE this

    def addToBalance(self, value):
        value = do_some_thing_with_value(value) # NOTE this
        self.balance += value

# example
accounttypeB.objects.create(balance=10,  name='Vincent Law', cls="accounttypeB")  
accounttypeA.objects.create(balance=9.5, name='Re-l Mayer', cls="accounttypeA")  
for obj in account.objects.all():
    obj.ext().addToBalance(1.0) 
    print(obj.name, obj.cls)

but you MUST create models using accounttypeA.objects.create(...) and accounttypeB.objects.create(...) - or else this trick will not work. (https://docs.djangoproject.com/en/1.5/topics/db/models/#multi-table-inheritance)