Django DRF返回过滤API对象时报TypeError:'type' object is not iterable

使用Django与Django REST Framework搭建活动展示类网站时，对数据库内现有模型做过滤、通过新增API返回过滤后对象遇到问题：直接返回数据库全量对象可正常运行，返回过滤后对象时触发报错 TypeError: 'type' object is not iterable。
当前暂未实现按日期过滤逻辑，先通过status字段测试过滤代码逻辑。

相关代码 #

models.py #

from django.db import models

class EventQuerySet(models.QuerySet):
    def today(self):
        return self.filter(status="Publish")


class EventManager(models.Manager):
    def get_queryset(self):
        return EventQuerySet(self.model, using=self._db)

    def today(self):
        return self.get_queryset().today()

class Event(models.Model):
    CATEGORY = (
        ('Smiles', 'Smiles'),
        ('Laughter', 'Laughter'),
        ('Crazy', 'Crazy'),
        ('Food', 'Food'),
        ('Outside', 'Outside'),
    )
    STATUS = (
        ('Publish', 'Publish'),
        ('Draft', 'Draft'),
    )
    title = models.CharField(max_length=200, blank=False)
    status = models.CharField(max_length=200, null=True, choices=STATUS)
    startDate = models.DateField(blank=True)
    endDate = models.DateField(blank=True)
    link = models.CharField(max_length=200, blank=False)
    category = models.CharField(max_length=200, null=True, blank=True, choices=CATEGORY)

    objects = models.Manager()
    date = EventManager()

    class Meta:
        unique_together = ('title', 'link')

    def __str__(self):
        return self.title

在python manage.py shell中测试上述查询逻辑可正常运行，返回结果示例：

<EventQuerySet [<Event: Positivus Festival 2022>, Central European zone stage in equestrian show jumping "Rīga 2022" >, <Event: Exhibition Dramaturgy of the Landscape>, <Event: Writing Implements of Medieval Riga>, '...(remaining elements truncated)...']> 

views.py #

代码参考Django官方Manager文档实现：

from events.models import Event
from rest_framework import generics
from rest_framework.generics import ListAPIView 
from events.serializers import EventSerializer
from django_filters import rest_framework as filters

class EventTodayView(ListAPIView):
    """
    API endpoint that allows events to be viewed or edited.
    """
    queryset = Event.date.today()

class EventFilter(filters.FilterSet):
    title = filters.CharFilter(field_name="title", lookup_expr='contains')
    startDate = filters.DateFilter(field_name="startDate", lookup_expr='gte')
    endDate = filters.DateFilter(field_name="endDate", lookup_expr='lte')

    class Meta:
        model = Event
        fields = ['title', 'status', 'startDate', 'endDate']


class EventAPIView(generics.ListAPIView):
    """
    API endpoint that allows events to be viewed or edited.
    """
    queryset = Event.objects.all().order_by('startDate')
    serializer_class = EventSerializer
    filter_backends = (filters.DjangoFilterBackend,)
    filterset_class = EventFilter

urls.py #

from django.contrib import admin
from django.urls import path

from events import views

urlpatterns = [
    path('admin/', admin.site.urls),
    path('api/', views.EventAPIView.as_view(), name='api'),
    path('api/today', views.EventTodayView.as_view(), name='api-today')
]

完整报错信息 #

Internal Server Error: /api/today
Traceback (most recent call last):
  File "D:\Prosjekter\Koding\What's happening\env\lib\site-packages\django\core\handlers\exception.py", line 55, in inner
    response = get_response(request)
  File "D:\Prosjekter\Koding\What's happening\env\lib\site-packages\django\core\handlers\base.py", line 197, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "D:\Prosjekter\Koding\What's happening\env\lib\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "D:\Prosjekter\Koding\What's happening\env\lib\site-packages\django\views\generic\base.py", line 84, in view
    return self.dispatch(request, *args, **kwargs)
  File "D:\Prosjekter\Koding\What's happening\env\lib\site-packages\rest_framework\views.py", line 509, in dispatch
    response = self.handle_exception(exc)
  File "D:\Prosjekter\Koding\What's happening\env\lib\site-packages\rest_framework\views.py", line 469, in handle_exception
    self.raise_uncaught_exception(exc)
  File "D:\Prosjekter\Koding\What's happening\env\lib\site-packages\rest_framework\views.py", line 480, in raise_uncaught_exception
    raise exc
  File "D:\Prosjekter\Koding\What's happening\env\lib\site-packages\rest_framework\views.py", line 506, in dispatch
    response = handler(request, *args, **kwargs)
  File "D:\Prosjekter\Koding\What's happening\env\lib\site-packages\rest_framework\generics.py", line 199, in get
    return self.list(request, *args, **kwargs)
  File "D:\Prosjekter\Koding\What's happening\env\lib\site-packages\rest_framework\mixins.py", line 38, in list
    queryset = self.filter_queryset(self.get_queryset())
  File "D:\Prosjekter\Koding\What's happening\env\lib\site-packages\rest_framework\generics.py", line 149, in filter_queryset
    for backend in list(self.filter_backends):
TypeError: 'type' object is not iterable

报错原因 #

1. 直接原因：EventTodayView未显式指定filter_backends属性，继承使用全局DRF配置的过滤后端时，全局配置的DEFAULT_FILTER_BACKENDS被错误赋值为过滤类本身（type类型），而非可迭代的元组/列表，导致遍历时报错。正常运行的EventAPIView因为显式定义了filter_backends = (filters.DjangoFilterBackend,)覆盖了全局错误配置，所以不受影响。
2. 潜在问题：直接在视图类属性层面赋值queryset = Event.date.today()会导致查询集在服务启动时就被评估固化，后续数据库的数据变更（新增/修改/删除活动）不会被该接口感知，同时可能存在ORM初始化时序问题。
3. 缺失配置：EventTodayView未指定serializer_class，即使修复过滤后端问题，后续也会触发序列化类缺失的报错。

修复方案 #

1. 修正EventTodayView代码 #

补全缺失的序列化类配置，重写get_queryset()方法返回动态查询结果，显式指定过滤后端配置避免全局配置影响：

class EventTodayView(ListAPIView):
    """
    API endpoint that returns published events.
    """
    serializer_class = EventSerializer
    # 该接口不需要额外过滤功能则配置为空元组，需要复用过滤逻辑可参考EventAPIView添加对应配置
    filter_backends = ()

    def get_queryset(self):
        return Event.date.today()

2. 修正全局DRF配置（可选，避免其他接口同类报错） #

打开项目settings.py找到REST_FRAMEWORK配置段，检查DEFAULT_FILTER_BACKENDS配置，确保其为可迭代的列表/元组格式，单个元素的元组末尾必须加逗号：

REST_FRAMEWORK = {
    # 其他原有配置...
    'DEFAULT_FILTER_BACKENDS': (
        'django_filters.rest_framework.DjangoFilterBackend',
    )
}

内容的提问来源于stack exchange，提问作者Erling