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When a function returns a queryset that is only annotated for a filter #3382
Description
I originally made this as a discussion but I get this feeling you don't get notifications for those. My apologies for the spam!
So in making my QuerySets defined as generic so that django-stubs starts to understand .annotate properly I have a problem where I don't want to always recognise that a queryset is annotated.
For example
def make_my_filtered_queryset(qs: MyQuerySet) -> MyQuerySet:
return qs.annotate(some_count=Count(....)).filter(some_count==1)After I make my queryset generic it starts to complain at me along the lines of
Incompatible return value type (got "MyQuerySet[MyModel@AnnotatedWith[TypedDict({'some_count': Any})], MyModel@AnnotatedWith[TypedDict({'some_count': Any})]]", expected "MyQuerySet[MyModel]") [return-value]
I'd rather not add several hundred TypedDicts for annotations that aren't relevant out of the immediate .filter that uses them.
I'm wondering what y'all think about this situation and whether it's reasonable for mypy to say an annotated queryset is a superset of it's unannotated equivalent?
Activity
sobolevn commentedon May 13, 2026
Indeed, I don't for some reason 😅
We can match this in theory for the return types. It is safe to return a more specific type that return annotation allows.
But, we can't match it in the parameter annotation.
So yeah,
qs.annotate(some_count=Count(....)).filter(some_count==1)is a more specific type ofqsAny ideas / PRs on how to do that are welcome :)
delfick commentedon May 16, 2026
@sobolevn
nice. Cause my question is about at runtime whether there is a difference in behaviour if the queryset is annotated or not. I'm not entirely sure.
I suppose it's a question of what mypy plugin hook would be relevant. And unless I'm mistaken, that comparison happens within mypy and we don't have a hook to override the type of the object that is used to determine what is returned from the function right?
Add hide_queryset_annotations helper
Add hide_queryset_annotations helper
Add hide_queryset_annotations helper
Add hide_queryset_annotations helper
delfick commentedon Jun 1, 2026
@sobolevn I think the reason mypy doesn't like it is because the type vars on a QuerySet appear both as inputs and outputs and so mypy doesn't recognise that querysets are read only. Though I made a version locally that removes that and it still doesn't like it, so maybe I'm wrong.
In the meantime I've added a feature to my plugin (across these two PRs, PR1, PR2) that lets me turn an annotated type into a non annotated type.
I'll use that so I can resolve the remaining 250 errors we get going from django-stubs 6.0.1 to 6.0.5 (and I'll see if there's any other oversights I've missed in this)
Is this something you'd be interested in including in django-stubs itself?
sobolevn commentedon Jun 1, 2026
@delfick yes, sounds great to have :)
But, I would prefer not to have
hide_queryset_annotations, but to have this feature built in :)(if this is possible, of course)
delfick commentedon Jun 1, 2026
@sobolevn what do you mean by "built in"?
sobolevn commentedon Jun 1, 2026
Ideally
qs.annotate(some_count=Count(....)).filter(some_count==1)should be compatible withMyQuerySetreturn type without any use code changes. BecauseMyQuerySet[MyModel@AnnotatedWith[TypedDict({'some_count': Any})], MyModel@AnnotatedWith[TypedDict({'some_count': Any})]]looks like a super type ofMyQuerySet[MyModel]delfick commentedon Jun 1, 2026
yeah, for sure. I imagine for that to work we'd need to create a strict subset of QuerySet that actually is read only. I imagine that would require a bunch of other work so that methods on such a type propagate such a readonly type though. And probs would result in a more awkward situation.