id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
31606	Cannot mix Exists expression with keyword arguments to When	Ryan Heard	nobody	"I don't seem to be able to provide an Exists expression to When alongside keyword arguments like you can with filter. For instance, consider:

{{{
class State(models.Model):
 pass

class County(models.Model):
  name = CharField(max_length=50)
  state = ForeignKey(State, related_name='counties')
}}}

I can execute the following query just fine:

{{{
County.objects.filter(
  Exists(State.objects.filter(counties=OuterRef('pk'), name=""Texas"")),
  name=""Dallas"",
)
}}}

But a similar query using When does not work:

{{{
>>> County.objects.annotate(
  status=Case(
    When(Exists(State.objects.filter(counties=OuterRef('pk'), name=""Texas"")), name=""Dallas"", then=Value(""DALLAS COUNTY"")),
    default=Value(""ELSEWHERE""),
))
}}}

Instead the arguments must be wrapped in a Q object:

{{{
>>> County.objects.annotate(
  status=Case(
    When(Q(Exists(State.objects.filter(counties=OuterRef('pk'), name=""Texas"")), name=""Dallas""), then=Value(""DALLAS COUNTY"")),
    default=Value(""ELSEWHERE""),
))
}}}

This is inconvenient and inconsistent with how filter works, as shown.

When's __init__ method can be modified to allow similar input as filter. [https://github.com/rheard/django/commit/978e796bb18414d995d515ab7923831149300977 Code is in a branch in my repo], but as this is my first time contributing to Django, I want to make sure I open a ticket and get feedback first."	Cleanup/optimization	new	Uncategorized	3.0	Normal				Unreviewed	1	0	0	0	1	0