带有查找字段的嵌套模型外键上的 Django JOIN答案

【问题标题】：Django JOIN on nested model Foreign key with look up field带有查找字段的嵌套模型外键上的 Django JOIN
【发布时间】：2018-03-12 19:00:08
【问题描述】：

我在 Django Rest Framework 中使用 2 个模型。

class Questions(models.Model):
    question = models.TextField()
    answer = models.TextField()
    timestamp = models.DateTimeField(auto_now_add=True)
    categories = models.ForeignKey(Categories, related_name="cat_questions", on_delete=models.CASCADE)


class QuestionnaireResult(models.Model):
    patient_info = models.ForeignKey(PatientInfo, related_name="+", on_delete=models.CASCADE)
    questions = models.ForeignKey(Questions, related_name="result_questions", on_delete=models.CASCADE)
    answer_given = models.TextField()
    timestamp = models.DateTimeField(auto_now_add=True)

两者都有序列化器：

class QuestionnaireResultSerailizer(serializers.ModelSerializer):
    class Meta:
        model = QuestionnaireResult
        fields = '__all__'


class QuestionsSerializer(serializers.ModelSerializer):
    result_questions = QuestionnaireResultSerailizer(many=True)

    class Meta:
        model = Questions
        fields ='__all__'

观看次数：

class QuestionsViewSet(viewsets.ModelViewSet):
    queryset = Questions.objects.all()
    serializer_class = QuestionsSerializer


class QuestionnaireResultViewSet(viewsets.ModelViewSet):
    queryset = QuestionnaireResult.objects.all()
    serializer_class = QuestionnaireResultSerializer
    filter_backends = (filters.DjangoFilterBackend,)
    filter_fields = ['patient_info']

使用 URL - http://localhost:9000/api/questions/1，它根据 question_id = 1 给出结果，result_questions 仅包含那些具有 questions id == 1。没错。

{
    "id": 1,
    "result_questions": [
        {
            "id": 1,
            "answer_given": "no",
            "timestamp": "2017-10-01T12:28:19.770454Z",
            "patient_info": 1,
            "questions": 1
        },
        {
            "id": 4,
            "answer_given": "no",
            "timestamp": "2017-10-01T13:13:19.658930Z",
            "patient_info": 2,
            "questions": 1
        }
    ],
    "question": "digestive ques 1",
    "answer": "yes",
    "timestamp": "2017-09-30T17:04:59.143857Z",
    "categories": 1
}

但上面 nested json (result_questions) 返回 all patient_info 其中有 questions id == 1 但我想添加一个更多过滤器（患者信息） 就可以了。我只想要那些我想通过传递为查找字段来检索的患者信息。

我想要的是那个。假设，我使用这个网址http://localhost:9000/api/questions/1?patient_info=1

它返回具有 question_id == 1 和 Patient_info ==1 的响应。因此，响应应该是：

{
    "id": 1,
    "result_questions": [
        {
            "id": 1,
            "answer_given": "no",
            "timestamp": "2017-10-01T12:28:19.770454Z",
            "patient_info": 1,
            "questions": 1
        }
    ],
    "question": "digestive ques 1",
    "answer": "yes",
    "timestamp": "2017-09-30T17:04:59.143857Z",
    "categories": 1
}

【问题讨论】：

也请发表您的看法
@JahongirRahmonov 已发布视图。

标签： mysql django serialization django-rest-framework foreign-keys

【解决方案1】：

你可以试试serializermethodfield

class QuestionsSerializer(serializers.ModelSerializer):
    result_questions = serializers.SerializerMethodField()

    class Meta:
        model = Questions
        fields ='__all__'

    def get_result_questions(self, obj):
        qs = obj.result_questions.all()
        request = self.context.get('request')
        patient_info = request.GET.get('patient_info')
        if patient_info:
            qs = qs.filter(patient_info=patient_info)
        return QuestionnaireResultSerailizer(qs, many=True).data

【讨论】：

谢谢。有效。你能帮我找到学习django rest框架的交互式教程吗？
很高兴为您提供帮助。我是通过django-angularjs-tutorial开始学习drf的
有一个问题。如果我使用serializers.SerializerMethodField()。我不能做POST 请求。它抛出错误 - "errors": "'NoneType' object has no attribute 'GET'"
对于发布操作，如果使用 SerializerMethodField，则需要覆盖 create 方法
或尝试理解@neverwalkaloner 的答案并修复错误

【解决方案2】：

在视图中尝试在get_object 方法中使用prefetch_related：

def get_object(self, pk):
    try:
        return Questions.objects.prefetch_related(Prefetch('result_questions',  
            queryset=QuestionnaireResult.objects.filter(id=self.request.GET.get('patient_info')))).get(pk=pk)
    except Questions.DoesNotExist:
        raise Http404

【讨论】：

它抛出 - get_object() takes exactly 2 arguments (1 given)