I have the following problem:
class species(models.Model):
pass
class question(models.Model):
species = models.ForeignKey(species)
class answer(models.Model):
question = models.ForeignKey(question)
Now I'd like to retrieve a queryset of species that contain any question that do not have any answers.
I mean I can get all species that have questions by using:
sp = species.objects.annotate(num_questions=Count('question')).filter(
num_questions__gt=0)
Also I can get all questions that do not have answers using:
qs = question.objects.annotate(num_answers=Count('answer')).filter(
num_answers=0)
But how do I combine the two things together?
thanks in advance!
You can daisy-chain annotations like so:
sp = species.objects.annotate(num_questions=Count('question')).annotate(
num_answers=Count('answer')).filter(num_questions__gt=0, num_answers=0)
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