Serialization of nested models in Django Rest Framework

Question

I have nested models and many to many relations. When I try to serialize them, results are not visible.

Tried everything in documentation and related names etc.

My base model is like this:

class Question(models.Model):
    ques_code = models.CharField(max_length=12, null=True, default='Ques Code')

    def __str__(self):
        return self.ques_code

Child Model is:

class MCQuestion(Question):
    answer_order = models.CharField(
        max_length=30, null=True, blank=True,
        choices=ANSWER_ORDER_OPTIONS,
        help_text=_("The order in which multichoice "
                    "answer options are displayed "
                    "to the user"),
        verbose_name=_("Answer Order"))

Then linked answer class with key as:

class Answer(models.Model):
    mcquestion = models.ForeignKey(MCQuestion,related_name='answers', on_delete=models.CASCADE)

    content = models.CharField(max_length=1000,
                               blank=False,
                               help_text=_("Enter the answer text that "
                                           "you want displayed"),
                               verbose_name=_("Content"))

    correct = models.BooleanField(blank=False,
                                  default=False,
                                  help_text=_("Is this a correct answer?"),
                                  verbose_name=_("Correct"))

    def __str__(self):
        return self.content

Serializers are as:

class AnswerSerializer(serializers.ModelSerializer):
    class Meta:
        model = Answer
        fields = ('content','correct')


class MCQuestionSerializer(serializers.ModelSerializer):
    answers = AnswerSerializer(many=True, read_only=True)
    #answers = serializers.SerializerMethodField()
    quiz = QuizSerializer(many=True)

    class Meta:
        model = MCQuestion
        fields = ('ques_code','answers')

Views are:

class QuestionViewSet(viewsets.ModelViewSet):
    queryset = Question.objects.all()
    serializer_class = MCQuestionSerializer

When I access API for questions, nested answers are not visible. I checked all documentation and checked and changed my code.

If I try using answers = serializers.SerializerMethodField() and define get_answers function for it, error comes saying "Question has no attribute of answers"

I think it is due to child and mother model system. It is searching attribute in Question, not in MCQuestion model. What can I do?

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

You were using the "wrong queryset-serializer combination" for the viewset class.

So, change the queryset reference in your view class as ,

class QuestionViewSet(viewsets.ModelViewSet):
    queryset = MCQuestion.objects.all()
    serializer_class = MCQuestionSerializer

Apart from that, I'm not sure you are aware of Django Model Inheritance. Anyway read it from here if necessary, Django Model Inheriitance

edited Jun 20, 2020 at 9:12

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answered May 3, 2019 at 14:21

JPG

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5 Comments

Himanshu Sharma Over a year ago

This gave me this error: django.db.utils.OperationalError: (1054, "Unknown column 'multichoice_answer.mcquestion_id' in 'field list'")

JPG Over a year ago

Did you migrated the db?

Himanshu Sharma Over a year ago

Yes , let me check code more if I am missing anything .. I have not included id anywhere in fields

JPG Over a year ago

The erros seems like you forgot to do the db migration

Himanshu Sharma Over a year ago

Got it ... done. Thanks. Works now. I changed the model .. migration doesn't work on existing data..

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