There are 2 simple models:
class Question(TimeStampedModel):
text = models.CharField(max_length=40)
class Answer(TimeStampedModel):
question = models.ForeignKey(Question, related_name='answers')
is_agreed = models.BooleanField()
author = models.ForeingKey(User, related_name='answers')
And there is my problem:
In [18]: Question.objects.count()
Out[18]: 3
I need to annotate queryset with 'is_user_agreed' and 'answers_amount' fields:
In [18]: user = User.objects.first()
In [19]: qs = Question.objects.annotate(
...: is_user_agreed=Case(
...: When(answers__in=user.answers.filter(is_agreed=True), then=Value(True)),
...: When(answers__in=user.answers.filter(is_agreed=False), then=Value(False)),
...: default=Value(None),
...: output_field=NullBooleanField(),
...: ),
...: ).annotate(answers_amount=Count('answers'))
...: qs.count()
Out[19]: 4
^ here count is 4, but I have only 3 questions in db :(
So, I've tried with distinct()
In [20]: qs.distinct().count()
Out[20]: 4 # but distinct doesn't work
In [21]: qs.distinct('id').count()
And after last line of code I've got this exception:
NotImplementedError: annotate() + distinct(fields) is not implemented.
I've also tried to use this trick annotate(Count('id')).filter(id__count__gt=1)
But in this case I'm losing all duplicate rows, and qs.count() is 2.
UPDATE: The problem is duplicated rows in queryset.
SOLUTION: (Extended variant of Vladimir's second approach)
user = User.objects.first()
user_agreed_questions = user.answers.filter(
is_agreed=True).values_list('question_id', flat=True)
user_not_agreed_questions = user.answers.filter(
is_agreed=False).values_list('question_id', flat=True)
Question.objects.annotate(
answer_amount=Count('answers'),
is_user_agreed=Case(
When(id__in=user_agreed_questions, then=True),
When(id__in=user_not_agreed_questions, then=False),
default=None,
output_field=NullBooleanField(),
),
)
See Question&Answers more detail:
os