python - 不显示使用 SerializerMethodField 添加的字段

Question

这些是我的模型.py

class Grade(models.Model):
    grade = models.CharField(max_length=255, primary_key=True)
class Student(models.Model):
    name = models.CharField(max_length=255) 
    grade = models.ForeignKey(grade, on_delete=models.CASCADE)
    rollno = models.BigIntegerField()

我想做的是制作一个序列化器，它使用网址“check/{str:pk}/”为我提供特定年级的所有学生的列表(以实现获取和删除方法)。在我的序列化器中，我尝试组合这两个模型并将它们显示在一起，如下所示:

class MySerializer(serializers.ModelSerializer):
    allStudents = serializers.SerializerMethodField()
    class Meta:
        model = Grade
        fields = ("grade", "allStudents")

    def get_allStudents(self, obj):
        s_list = []
        fields = ['name', 'grade', 'rollno']
        for stds in obj:
            s_list.append(model_to_dict(stds, fields=fields))
        return s_list

我的views.py 看起来如下:

class IndividualGrade(generics.RetrieveUpdateDestroyAPIView):
    '''
    PUT check/{grade}/
    GET check/{grade}/
    DELETE check/{grade}/
    '''
    queryset = Grade.objects.all()
    serializer_class = MySerializer

    def get(self, request, *args, **kwargs):  
        try:
            s1 = Grade.objects.get(grade=kwargs["pk"])
            all_stds = Student.objects.filter(grade=s1) 
            a_grade = Grade.objects.get(grade=s1)
            return Response(MySerializer(a_grade, all_stds ).data)
        except Grade.DoesNotExist:
            return Response(
                data={
                    "message": "Grade with id: {} does not exist".format(kwargs["pk"])
                },
                status=status.HTTP_404_NOT_FOUND
            )

    def delete(self, request, *args, **kwargs):        
        try:
            Grade.objects.get(grade=kwargs["pk"]).delete()
            return Response(status=status.HTTP_204_NO_CONTENT)            
        except Grade.DoesNotExist:
            return Response(
                data={
                    "message": "Grade with id: {} does not exist".format(kwargs["pk"])
                },
                status=status.HTTP_404_NOT_FOUND
            )

这给了我以下错误:

"message": "Grade with id: grade9 does not exist"

虽然条目肯定存在。因为我可以删除它，所以它不会显示添加的字段。

当涉及到不是直接的序列化器时，我真的很天真。

还是不知道我做错了什么。另外，我想知道是否可以在 SerializerMethodFiled 中使用另一个序列化器

编辑1. 更新放置请求:http://127.0.0.1:8000/check/grade5/

JSON 输入:

{
    "grade": "grade5",
    "allstudents": [
        {
            "name": "Shub",
            "grade": "grade5",
            "rollno": 4
        }
    ]
}

Answer 1

我认为您在编写代码时并没有理解什么是SerializerMethodField。您无需传递任何额外内容即可使用 SerializerMethodField 获取值。这意味着，您不需要将 all_stds 作为 MySerializer 的参数传递。因此，您应该像这样更新序列化器:

class StudentSerializer(serializers.ModelSerializer):
    class Meta:
        model = Student
        fields = ('name', 'grade', 'rollno')


class MySerializer(serializers.ModelSerializer):
    def get_allStudents(self, obj):
        # here obj is a Grade Object
        # we can get all the students by `obj.student_set.all()` via reverse relationship
        return StudentSerializer(obj.student_set.all(), many=True).data

此外，当您使用 RetriveUpdateDestroyApiView 时，它将处理所有 get、patch、put、delete 方法。您不需要在 View 中覆盖它们。因此以下代码足以满足您的需求。

class IndividualGrade(generics.RetrieveUpdateDestroyAPIView):
    '''
    PUT check/{grade}/
    GET check/{grade}/
    DELETE check/{grade}/
    '''
    queryset = Grade.objects.all()
    serializer_class = MySerializer

    # No more code is needed