Syntax Error when combining __in and F() in filter

[Douglas Franklin]

Similar to https://code.djangoproject.com/ticket/32151

I have a simple Google Calendar Events application. Profiles generate calendar tokens with GSuite Oauth (not shown) that are used to make CalendarEvents in my database (postgres:9.6). CalendarEvents queried via a particular CalendarToken have the token's profile on the model. See oversimplified example below:

class Profile(models.Model):
    name = models.CharField(max_length=32)

class CalendarEvent(models.Model):
   profile = models.ForeignKey(Profile, on_delete=models.CASCADE)
   attendees = models.ManyToManyField(Profile, on_delete=models.CASCADE)

I'm trying to annotate whether a profile is "attending" the event, by checking if the profile is in the attendees ManyToMany:

CalendarEvent.objects.annotate(
    is_attending=Case(
        When(
            profile__in=F('attendees'),
            then=Value(True)
        ),
        default=Value(False),
        output_field=models.BooleanField()
    )
)

Generates an invalid syntax error (replacing db name with {APP}):

ProgrammingError: syntax error at or near ""{APP}_calendarevent_attendees""
LINE 1: ...CASE WHEN ("{APP}_calendarevent"."profile_id" IN "{APP}_ca...