Does .filter(somefield__isnull=False) not work for what you're trying to do?
On Thursday, August 7, 2014 7:43:07 PM UTC-4, David Butler wrote: > > It would be nice if there was some database level optimization for getting > objects that have related objects that exist. > > This is a slow filter: > > qs = [obj for obj in qs if qs.somefield_set.exists()] > > Could be faster with something like this: > > qs = qs.filter(somefield__exists=True) > > Here is some (rough, probably grossly over simplified but working) code: > > Code is also available here if it gets garbled: http://dpaste.com/0825PNP > > > query_template = ( > '{not_part} EXISTS (SELECT 1 FROM "{table1}" WHERE ' > '"{table1}"."{table1_column}" = "{table2}"."{table2_column}")' > ) > def filter_by_reverse_feriegn_key_existance(qs, **kw): > > for arg, value in kw.items(): > > assert arg.endswith('__exists') > > if value is True: > not_part = '' > elif value is False: > not_part = 'NOT' > > Model = qs.model > for field in arg.rstrip('__exists').split('__'): > field = Model._meta.get_field_by_name(field)[0] > > qs = qs.extra(where=[query_template.format( > table1=field.model._meta.db_table, > table1_column=field.field.db_column, > table2=Model._meta.db_table, > table2_column=Model._meta.pk.db_column, > not_part = not_part > )]) > > Model = field.model > return qs > > > This works on postgres, and is ~100x faster > > I would be interested in any comments > -- You received this message because you are subscribed to the Google Groups "Django developers" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/django-developers. To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/cce7a4cb-d452-45e9-8ea3-ffd8a949f0c9%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
