On Thu, 2007-11-01 at 11:35 -0700, Andy Brody wrote:
> Ah, thanks for the values() hint. It seems to work decently. I don't
> really need to access related model fields, I just want a list of
> unique group objects associated with a given musician's activities.
>
> The above becomes instead:
>
> qset = theMusician.activity_set.all().values('group').distinct()
> # returns list of {'group': id} without duplicates
>
> grouplist = [Group.objects.get(id=valuesdict['group']) for valuesdict
> in qset]
If efficiency was a concern, this does a lot of queries (len(qset) of
them). Instead, try
grouplist = Group.objects.filter(id__in=[(d['group'] for d in
qset])
which constructs grouplist with only one extra query.
> Or maybe it would be better to leave the duplicates testing in python:
>
> grouplist = [act.group for act in theMusician.activity_set.all()]
> group_ids = []
> for group in grouplist[:]:
> if group.id in group_ids:
> grouplist.remove(group)
> else:
> group_ids.append(group.id)
>
> Why doesn't set(grouplist) remove the duplicates, anyway?
Because the instances aren't the same even when the id values are the
same. get() returns a *new* instance each time.
> Do these both make sense? Would one hit the database less than the
> other?
My modified solution is probably fastest for what you can do at the
moment without custom SQL. Two SQL queries and one list comprehension in
Python.
Regards,
Malcolm
--
What if there were no hypothetical questions?
http://www.pointy-stick.com/blog/
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