如何组合来自两个模型的两个查询集？ Django 休息框架答案

【问题标题】：How to combine two querysets from two models? Django Rest Framework如何组合来自两个模型的两个查询集？ Django 休息框架
【发布时间】：2022-02-03 03:39:00
【问题描述】：

我有两个模型

class Answer(models.Model):
    answer = models.TextField()
    created_at = models.DateTimeField(editable=False, default=timezone.now)
    updated_at = models.DateTimeField(default=timezone.now)
    user = models.ForeignKey('users.CustomUser', on_delete=models.PROTECT)
    question = models.ForeignKey('Question', on_delete=models.PROTECT)
    number_of_points = models.IntegerField(default=0)
    moderate_status = models.BooleanField(default=False)

和

class Question(models.Model):
    question_subject = models.TextField()
    question_text = models.TextField(default=None, null=True, blank=True)
    slug = models.SlugField(max_length=128, unique=True, null=False, editable=False)
    created_at = models.DateTimeField(editable=False, default=timezone.now)
    updated_at = models.DateTimeField(default=timezone.now)
    user = models.ForeignKey('users.CustomUser', on_delete=models.PROTECT)
    animal = models.ForeignKey('animals.Animal', on_delete=models.PROTECT)

序列化器.py

class QuestionDetailSerializer(serializers.ModelSerializer):
    answers = serializers.PrimaryKeyRelatedField(many=True, read_only=True)

    class Meta:
        model = Question
        fields = '__all__'

views.py

class QuestionsDetailView(generics.ListAPIView):
    queryset = Question.objects.all()
    serializer_class = QuestionsSerializer

    def get_queryset(self):
        return super().get_queryset().filter(
            id=self.kwargs['pk']
        )

url.py

path('questions/<int:pk>', QuestionsDetailView.as_view()),

我想组合 2 个查询集，一个已经通过 url 中提供的 pk 过滤问题，而我想提供的另一个查询集是 Answer.objects.all().filter(question__id='pk '）。本质上，我想显示所有问题以及特定问题的答案。

【问题讨论】：

标签： python django django-rest-framework django-views

【解决方案1】：

我强烈建议在任何可能的地方使用关系。

在models.py 中添加related_name 到Answer.question：

class Answer(models.Model):
    ...
    question = models.ForeignKey('Question', on_delete=models.PROTECT, related_name='answers')

如果id在序列化器中足够了，那么在serializers.py中：

class QuestionDetailSerializer(serializers.ModelSerializer):
    # this is not needed anymore: answers = serializers.PrimaryKeyRelatedField(many=True, read_only=True)

    class Meta:
        model = Question
        fields = ['question_subject ', 'question_text', ..., 'answers`]

但是你也可以创建一个model 的函数，你可以用类似的方式包含它：

class Question(models.Model):
    ...
    def get_answers(self):
        return [answer.answer for answer in self.answers.all()]    # it will return a list of TextFields of answers

serializers.py:

class QuestionDetailSerializer(serializers.ModelSerializer):
    class Meta:
        model = Question
        fields = ['question_subject ', 'question_text', ..., 'get_answers`]

【讨论】：

【解决方案2】：

您不会完全组合来自不同表的 2 个查询集。但是你可以使用嵌套的序列化器。

class AnswerSerializer(serializers.ModelSerializer):

    class Meta:
        model = Anwser
        fields = ['id', ...]

class QuestionDetailSerializer(serializers.ModelSerializer):
    answer_set = AnswerSerializer(many=True, read_only=True)

    class Meta:
        model = Question
        fields = ['id', ..., 'answer_set']

# OR


class QuestionDetailSerializer(serializers.ModelSerializer):

    class Meta:
        model = Question
        fields = ['id']
    
    def to_representation(self, instance):
        data = super().to_representation(instance)
        data['answers'] = AnswerSerializer(many=True, instance=instance.anwser_set.all()).data
        return data

【讨论】：