Django excluding specific instances from queryset without using field lookup

Agos picture Agos · Jun 13, 2010 · Viewed 38.6k times · Source

I sometimes have the need to make sure some instances are excluded from a queryset.
This is the way I do it usually:

unwanted_instance = MyModel.objects.get(pk=bad_luck_number)
uninteresting_stuff_happens()
my_results = MyModel.objects.exclude(id=unwanted_instance.id)

or, if I have more of them:

my_results = MyModel.objects.exclude(id_in=[uw_in1.id, uw_in2.id, uw_in3.id])

This 'feels' a bit clunky, so I tried:

my_ideally_obtained_results = MyModel.objects.exclude(unwanted_instance)

Which doesn't work. But I read here on SO that a subquery can be used as parameter for exclude.
Am I out of luck? Am I missing some functionality (checked the docs, but didn't find any useful pointer)

Answer

obeattie picture obeattie · Jun 13, 2010

The way you're already doing it is the best way.

If it's a model-agnostic way of doing this you're looking for, don't forget that you can do query.exclude(pk=instance.pk).

Just as an aside, if Django's ORM had an identity mapper (which it doesn't at present), then you would be able to do something like MyModel.objects.filter(<query>).all().remove(<instance>), but you're out of luck in that regard. The way you're doing it (or the one above) is the best you've got.

Oh, and also you can do much better than that in query with a list comprehension: query.exclude(id__in=[o.id for o in <unwanted objects>])