Hi,
I was looking for an easy way to define extra outer joins. It
turned out that it's easy to extend the QuerySet.extra method
with a 'joins' argument used like this:
notes = Note.objects.select_related().extra(
joins=['''left outer join %s rel1 on
rel1.id=%s.release_beginn_id'''
% (Release._meta.db_table, Note._meta.db_table),
'''left outer join %s rel2 on
rel2.id=%s.release_behoben_id'''
% (Release._meta.db_table, Note._meta.db_table)],
where=['''((%(notes_table)s.release_beginn_id is null or
rel1.sort_value <= %(sort_value)d)
and (%(notes_table)s.release_behoben_id is null or
rel2.sort_value > %(sort_value)d))'''
% {'sort_value': version, 'notes_table':
Note._meta.db_table}])
(I left out the db name quoting since it doesn't contribute much
to this example.)
The patch is surprisingly small:
http://code.djangoproject.com/attachment/ticket/2922/extra_joins.diff
I guess this is currently under a freeze. I just wanted to bring
it up for discussion. If there's serious interest, I can flesh it
out (docs, testcases) later when the winter^H^H^H^H^H^H^H freeze
is over.
Michael
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