Consider something like a tag hierarchy model:
class Tag(models.Model):
name = models.CharField(maxlength = 50, unique = True)
parent = models.ForiegnKey('self', related_name='child',
null = True, blank = True)
class Meta:
ordering = ['parent', 'name']
def __str__(self):
if self.parent_id is not None:
prefix = str(self.parent) + '/'
else:
prefix = ''
return prefix + self.name
Now, this model almost, but not quite, orders the tags in a "natural"
fashion. That is, if I have a tag structure that looks like this:
Life
Universe
Everything
Software
Python
Django
Design
Theory
I will get an ordering of:
Life
Software
Life/Everything
Life/Universe
Software/Design
Software/Python
Software/Design/Theory
Software/Python/Django
(actually, for some reason that I don't yet understand and suspect is a
bug, I don't get the ordering in the admin list view, but it does get
ordered that way in select boxes and stuff that I care about. Let's
ignore that for now.)
What I really want is for the ordering to have sub-categories under the
parent category. This would be easy if I could sort on the str() value
for each object, since the natural ordering is the lexicographic
ordering of the strings. Is there an easy way to do this? I seem to have
come across it a few times now (I like hierarchies, so sue me).
Unfortunately, Meta.ordering seems to want a real field, not a method
(which Admin.list_display can take) or a property.
So am I missing something, or is this even a common need for other
people?
Malcolm
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