How to do Django Rest Framework double nested serializer - serialization

Question

I'm trying to build an api that have an endpoint which in the POST receives the JSON like bellow:
{
"title":"Quiz 1",
"questions":[
{
"description":"Question 1?",
"answers":[
{
"description":"Answer 1",
"true_or_false":true
},
{
"description":"Answer 2",
"true_or_false":false
}
]
},
{
"description":"Question 2?",
"answers":[
{
"description":"Answer 1",
"true_or_false":true
},
{
"description":"Answer 2",
"true_or_false":false
}
]
}
]
}
But I don't know how to build the serializers for double nested fields, like a list of answers within a question and a list of questions within a quiz. The code I made so far is below:
models.py
from django.db import models
class Quiz(models.Model):
title = models.CharField(max_length=200, blank=False)
def __str__(self):
return self.title
class Question(models.Model):
description = models.CharField(max_length=10000, blank=False)
quiz = models.ForeignKey(Quiz, related_name='questions', on_delete=models.CASCADE, default=None)
def __str__(self):
return self.description
class Answer(models.Model):
question = models.ForeignKey(Question, related_name='answers', on_delete=models.CASCADE)
description = models.CharField(max_length=1000, blank=False)
true_or_false = models.BooleanField(default=False, blank=False)
def __str__(self):
return self.description
views.py
class QuestionViewSet(viewsets.ModelViewSet):
queryset = Question.objects.all()
serializer_class = QuestionSerializer
class AnswerViewSet(viewsets.ModelViewSet):
queryset = Answer.objects.all()
serializer_class = AnswerSerializer
class QuizViewSet(viewsets.ModelViewSet):
queryset = Quiz.objects.all()
serializer_class = QuizSerializer
class OnlyQuizViewSet(generics.ListAPIView):
def get_queryset(self):
queryset = Quiz.objects.filter(id=self.kwargs['pk'])
return queryset
serializer_class = QuizSerializer
serializers.py
class AnswerSerializer(serializers.ModelSerializer):
class Meta:
model = Answer
fields = ['id', 'description', 'true_or_false']
class QuestionSerializer(serializers.ModelSerializer):
answers = AnswerSerializer(many=True)
class Meta:
model = Question
fields = ['id','description','answers']
read_only_fields = ('quiz',)
def create(self, validated_data):
answers_data = validated_data.pop('answers')
question = Question.objects.create(**validated_data)
for answer in answers_data:
Answer.objects.create(question=question, **answer)
return question
class QuizSerializer(serializers.ModelSerializer):
questions = QuestionSerializer(many=True)
class Meta:
model = Quiz
fields = ['id', 'title', 'questions']
def create(self, validated_data):
questions_data = validated_data.pop('questions')
quiz = Quiz.objects.create(**validated_data)
for questions in questions_data:
Question.objects.create(quiz=quiz, **questions)
return quiz
With the above serializers, I'm getting the error below:
Direct assignment to the reverse side of a related set is prohibited. Use answers.set() instead.
So what's the right way to build double-nested serializers? So far I haven't been able to find anything to help me

Answer 1

I'm gonna assume you get that error when you try posting to the Quiz api, you'll have a problem when you want to create a question
Question.objects.create(quiz=quiz, **questions)
since this question also includes a list of answers that needs to be created first.
Try using the serializer you already have like this
class QuizSerializer(serializers.ModelSerializer):
questions = QuestionSerializer(many=True)
class Meta:
model = Quiz
fields = ['id', 'title', 'questions']
def create(self, validated_data):
questions_data = validated_data.pop('questions')
quiz = Quiz.objects.create(**validated_data)
for questions in questions_data:
question_serializer = QuestionSerializer({**questions, "quiz": quiz}) # might need to send quiz.id instead
question_serializer.is_valid()
question_serializer.save()
return quiz
and update your QuestionSerializer to use AnswerSerializer the same way (or you can create Answers explicitly there)