DRF序列化器更新嵌套对象列表

Question

我使用 Django-rest-framework 编写投票应用程序项目。它有两种模型：问题和嵌套答案。我想根据请求更新有问题的序列化器的答案，例如：

{
    "question":"question",
    "answers": [{"answer":"first updated answer"}, {"answer":"second update answer"}]
}

我怎样才能正确地做到这一点？我尝试这样做，但我删除了每个请求中的答案并创建新的答案，因为每次都会更改它们的 id。

序列化器.py

class QuestionSerializer(serializers.ModelSerializer):
    user = serializers.StringRelatedField()
    answers = AnswerSerializer(many=True)

    class Meta(object):
        model = Question
        fields = ('id', 'question', 'answers', 'total_votes', 'user')
        read_only_fields = ('id', 'total_votes', )

    def update(self, instance, validated_data):
        instance.question = validated_data.get('question', instance.question)
        instance.save()

        question = Question.objects.get(id=instance.id)
        Answer.objects.filter(question=question).delete()

        answers_data = validated_data.pop('answers')
        for answer_data in answers_data:
            Answer.objects.create(question=question, **answer_data)

        return instance

模型.py

class Question(models.Model):
    question = models.CharField(verbose_name='Question', max_length=255)
    total_votes = models.IntegerField(verbose_name='Total Votes', default=0)
    user = models.ForeignKey(User, verbose_name='Owner', on_delete=models.CASCADE)

class Answer(models.Model):
    question = models.ForeignKey(Question, verbose_name='Question', related_name='answers',
                                 on_delete=models.CASCADE)
    answer = models.CharField(verbose_name='Answer', blank=True, max_length=255)
    votes_count = models.IntegerField(verbose_name='Count of Votes', default=0)

Answer 1

经过几个小时的文档浏览后才想到这一点：

序列化器.py

class AnswerSerializer(serializers.ModelSerializer):

    # this is IMPORTANT, without this the 'id' field won't appear in validated data
    id = serializers.IntegerField(required=False, write_only=False)

    class Meta:
        model = Answer

class QuestionSerializer(serializers.ModelSerializer):

    user = serializers.StringRelatedField()
    answers = AnswerSerializer(many=True)

    def update(self, instance, validated_data):
        answer_data = validated_data.pop("answers")

        remove_items = { item.id: item for item in instance.answers.all() }

        for item in answer_data:
            item_id = item.get("id", None)

            if item_id is None:
                # new item so create this
                instance.answers.create(**item)
            elif remove_items.get(item_id, None) is not None:
                # update this item
                instance_item = remove_items.pop(item_id)
                Answer.objects.filter(id=instance_item.id).update(**item)

        for item in remove_items.values():
            item.delete()

        for field in validated_data:
            setattr(instance, field, validated_data.get(field, getattr(instance, field)))
        instance.save()

        return instance