Hello,
I've been looking into trying to order a relation based on some
arithmetic on each model's fields. This would ideally be at a database
level, and not a brute force python way. A simple example which I
can't seem to get to work is a sum of two fields.
For example, I want to sum a total amount of votes both good and bad
on some user submission. The solution I thought of would involve
something like:
query_set = UserSubmission.objects.all()
query_set.annotate(total_votes=F('bad_vote_count') + F
('good_vote_count'))
query_set = query_set.order_by('-total_votes')
However I can't get past the annotation part. F expressions seem to
work inside a filter method call, but fail miserably inside an
annotation.
" 'ExpressionNode' object has no attribute 'lookup' ".
Even if this is a bug (according to ticket 10972), I'm wondering if
there's any other possible solutions, or if I'm approaching this
problem completely the wrong way.
Thanks for your time in advance,
- Eric
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