CODEWITHSUNDEEP
djangodjango-rest-framework
Desiigner
Desiigner

Reputation: 2316

Serialize foreign key's foreign key (DRF)

I have 3 levels of models: Question Session (contains a bunch of questions), Question and Answer. They all are connected via ForeignKey:

class QuestionSession(models.Model):
    name = models.CharField(max_length=100)

class Question(models.Model):
    description = models.CharField(max_length=400)
    question_type = models.CharField(max_length=50)
    answers = models.PositiveIntegerField(default=0)
    answers_to_close = models.PositiveIntegerField(default=3)
    answered = models.BooleanField(default=False)
    choices = models.CharField(
        max_length=1000, blank=True, null=True, default=None)

    question_session = models.ForeignKey(
        QuestionSession,
        on_delete=models.CASCADE,
        related_name='questions',
        blank=True,
        null=True,
        default=None
    )

class Answer(models.Model):
    question = models.ForeignKey(
        Question,
        related_name='answers_list',
        on_delete=models.CASCADE)
    answer = models.CharField(max_length=500)
    created_at = models.DateTimeField(auto_now_add=True)

And my serializers.py:

class QuestionSessionSerializer(serializers.ModelSerializer):
project = ProjectSerializer()

class Meta:
    model = QuestionSession
    fields = [
        'id',
        'questions',
        'project'
    ]


class QuestionSerializer(serializers.ModelSerializer):
    question_session = QuestionSessionSerializer()

class Meta:
    model = Question
    fields = [
        'id',
        'description',
        'question_type',
        'created_at',
        'answers',
        'answers_to_close',
        'answered',
        'question_session',
        'choices',
        'answers_list'
    ]


class AnswerSerializer(serializers.ModelSerializer):
    question = QuestionSerializer()

class Meta:
    model = Answer
    fields = [
        'question',
        'answer',
        'created_at'
    ]

I can easily get question objects from QuestionSession with:

QuestionSession.objects.get(pk=1).questions.all()

And I'm also able to get answers with the following:

QuestionSession.objects.get(pk=1).questions.objects.get(pk=1).answers_list.all()

But when I send this data through Response, it only sends answers' ids instead of objects. My view:

    def get(self, request, **kwargs):
    """Fetch a single session"""

    session_id = kwargs['session_id']

    questions = QuestionSerializer(
        QuestionSession.objects.get(
            pk=session_id).questions.filter(answered=False),
        many=True
    )

    return Response({
        'session': session_id, 'questions': questions.data
    })

How can I modify my serializers to pass Answer objects instead of just id?

Upvotes: 4

Views: 1939

Answers (2)

Sakthi Panneerselvam
Sakthi Panneerselvam

Reputation: 1397

Using depth will solve the problem, but try to use prefetch_related and select_related. That will be best practice and it will reduce no queries(Query response is faster).

For your problem use select_related, it will solve the problem. For further reference or doubts use this link: https://medium.com/quant-five/speed-up-django-nested-foreign-key-serializers-w-prefetch-related-ae7981719d3f

P.S: For checking use Django Debug toolbar, it will explain how much subqueries are running in background.

Upvotes: 1

HuLu ViCa
HuLu ViCa

Reputation: 5450

Have you tried to specify nested depth on your serializer?:

class QuestionSerializer(serializers.ModelSerializer):
    question_session = QuestionSessionSerializer()

    class Meta:
        model = Question
        fields = [
            'id',
            'description',
            'question_type',
            'created_at',
            'answers',
            'answers_to_close',
            'answered',
            'question_session',
            'choices',
            'answers_list'
        ]
        depth = 1

Upvotes: 2

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