Question

I have:

class Foo(models.Model):
    pass

class Bar(Foo):
    pass

class Corn(Foo):
    pass

# Now I have these objects in the database:
john = Corn()
mary = Corn()
joe = Bar()
grace = Corn()
randy = Bar()

In Django, I use this to get a list of Foo objects:

foos = Foo.objects.all()

Now, how do I check if an object in foos list above is a Bar or a Corn?

for x in foos:
    print x.__class__.__name__ # returns Foo

Answer 1

Model inheritance won’t automatically return the subclass instances — if you ask the ORM for Foos, it will give you Foos. You need to ask if there is a Bar object with the same primary key:

for x in foos:
   Bar.objects.filter(pk=x.pk).exists() # True if it's a Bar, too
   Corn.objects.filter(pk=x.pk).exists() # True if it's a Corn, too

You can also use the model name (in lowercase) as an attribute, which will do the lookup for you, but it’s not guaranteed to succeed (obviously), so you need to guard against DoesNotExist exceptions:

for x in foos:
    try:
        x.bar
        # it's a bar
    except Bar.DoesNotExist:
        # it's not a bar
        pass
    try:
        x.corn
        # it's a corn
    except Corn.DoesNotExist:
        # it's not a corn
        pass