Hallöchen!
Tim Shaffer writes:
> [...]
>
>>>> 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()
You're right that this would contradict Django's documented
behaviour, which is efficient and well-defined. However, it is not
practical in presence of abstract base classes.
Consider the following scenario:
Author, Editor, and Translator are all derived from Person. No
person actually is "Person". "Person" is simply the common base
class. Then you want to list all contributors on a web page in a
table. The first column is the name -- that simple, because it is
an attribute. The second column is the result of "do_something()".
This wouldn't work, because the dynamic binding doesn't work in
Django:
{% for person in persons %}
<tr><td>{{ person.name }}</td><td>{{ person.do_something }}</td></tr>
{% endfor %}
My use case is somewhat different, by the way: I'd like to apply a
specially-tailored template to the instance whose name is derived
from the instance's model name. This doesn't work in vanilla
Django.
Mostly, though, you are only interested in the base class
attributes, so Django's behaviour is okay. Additionally, fetching
the actual instance for each instance is costly.
The cleanest solution is a contenttype attribute which contains the
actual model.
Tschö,
Torsten.
--
Torsten Bronger, aquisgrana, europa vetus
Jabber ID: torsten.bron...@jabber.rwth-aachen.de
or http://bronger-jmp.appspot.com
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