On Apr 21, 9:28 am, Tom Evans <tevans...@googlemail.com> wrote:
> On Wed, Apr 21, 2010 at 2:15 PM, Tim Shaffer <t...@tim-shaffer.com> wrote:
> > On Apr 21, 8:25 am, Torsten Bronger <bron...@physik.rwth-aachen.de>
> > wrote:
> >> calls the method of the respective class of "instance". However, in
> >> Django,
>
> >> for instance in RootClass.objects.all():
> >> instance.do_something()
>
> >> will *always* call RootClass.do_something(), which is almost never
> >> what you want.
>
> > I don't necessarily think that's a problem at all. That's the way it
> > should work. You want to be able to call RootClass.do_something() on
> > an instance of RootClass and have it run that method from one of the
> > sub classes?
>
> Yes please; this is called 'polymorphism', and is quite a neat
> feature. If I were to run:
>
> instance = Derived()
> instance.func()
>
> then I would want Derived.func to be executed. If, however, I wrote this:
>
> instance = Derived()
> Base.func(instance)
>
> then I would expect Base.func to be executed.
I think I must be missing something, because I'm pretty sure Django
doesn't change any of that.
Given the following example....
class Author(models.Model):
first = models.CharField(u'First Name', max_length=20)
last = models.CharField(u'Last Name', max_length=20)
def do_something(self):
print "I'm going to write"
class Translator(Author):
language = models.CharField(max_length=10)
def do_something(self):
print "I'm going to translate"
class Editor(Author):
language = models.CharField(max_length=10)
def do_something(self):
print "I'm going to edit"
>>> a = Author(first="Tim", last="Shaffer")
>>> a.translator = Translator(language="English")
>>> a.editor = Editor(language="German")
>>> t = Translator.objects.all()[0]
This works as I would expect it to...
>>> a.do_something()
"I'm going to write"
>>> t.do_something()
"I'm going to translate"
>>> Author.do_something(t)
"I'm going to write"
Calling a.do_something() should *never* call either
Translator.do_something() or Editor.do_something()
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