python - TypeError：__str__ 返回非字符串（NoneType 类型） - Django

Question

尝试提出数据列表请求时出现错误：

我的模型：

import uuid
import time

from django.db import models
from a.models import ModelA
from b.models import ModelB


def upload_location(instance, filename):
    filebase, extension = filename.split('.')
    milliseconds = int(round(time.time() * 1000))

    return 'a_id__%s/%s__%s.%s' % (instance.a_id, instance.name, milliseconds, extension)


class Attachment(models.Model):
    id = models.UUIDField(primary_key=True, unique=True, default=uuid.uuid4, editable=False, null=False)
    name = models.CharField(max_length=150)
    file = models.FileField(upload_to=upload_location)

    a = models.ForeignKey(
        ModelA,
        null=True,
        blank=False,
        on_delete=models.CASCADE
    )
    b = models.ForeignKey(
        ModelB,
        null=True,
        blank=False,
        on_delete=models.CASCADE
    )

    def __str__(self):
        return self.name

错误：

我尝试了以下方法，但没有成功...

    def __str__(self):
        return str(self.name)

    def __str__(self):
        return self.name or ''

    def __str__(self):
        return self.get_full_name

当我尝试通过“Django-Admin”打开屏幕以附加新项目时，会发生此错误

Answer 1

冲突的序列化程序

当我使用两个不同的序列化器进行列表时遇到了同样的错误。

我只需要删除行 serializer_class = Serializer_one

class SomeViewSet(viewsets.ViewSet):
    # serializer_class = Serializer_one
    def list(self, request):
        .....
        ........
        serializer = Serializer_two(some_queryset, many=True)
        return Response(serializer.data)