django 类型错误“银行”模型对象不可迭代

Question

我正在尝试创建列表和详细 api 视图。我有超过 100K 对象的数据库

模型.py

from django.db import models

# Create your models here.
class Banks(models.Model):
    name = models.CharField(max_length=49, blank=True, null=True)
    id = models.BigIntegerField(primary_key=True)

    class Meta:
        managed = False
        db_table = 'banks'


class Branches(models.Model):
    ifsc = models.CharField(primary_key=True, max_length=11)
    bank = models.ForeignKey(Banks, models.DO_NOTHING, blank=True, null=True)
    branch = models.CharField(max_length=250, blank=True, null=True)
    address = models.CharField(max_length=250, blank=True, null=True)
    city = models.CharField(max_length=50, blank=True, null=True)
    district = models.CharField(max_length=50, blank=True, null=True)
    state = models.CharField(max_length=26, blank=True, null=True)

    class Meta:
        managed = False
        db_table = 'branches'

序列化器.py

from rest_framework import serializers
from .models import Branches, Banks

class BankSerializer(serializers.ModelSerializer):
    class Meta:
        model = Banks
        fields= ['name', 'id']


class BranchSerializer(serializers.ModelSerializer):
    bank = BankSerializer(many=True,read_only=True)
    class Meta:
        model = Branches
        fields= ['ifsc','bank','branch','address','city','district','state']

views.py

from rest_framework import viewsets
from .serializers import BranchSerializer
from rest_framework import viewsets
class BankViewSet(viewsets.ModelViewSet):
    """
    API endpoint that allows users to be viewed.
    """
    queryset = Branches.objects.all()
    serializer_class = BranchSerializer

我尝试使用 .get_queryset()、.filter() 代替 .all() 但它仍然抛出错误

error datail
    Request Method: GET
    Request URL: http://127.0.0.1:8000/bankdetailapi/

Django Version: 3.2.3
Python Version: 3.9.5
Installed Applications:
['django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'api',
 'rest_framework',
 'corsheaders',
 'django_filters']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']



Traceback (most recent call last):
  File "C:\Python39\lib\site-packages\django\core\handlers\exception.py", line 47, in inner
    response = get_response(request)
  File "C:\Python39\lib\site-packages\django\core\handlers\base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Python39\lib\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "C:\Python39\lib\site-packages\rest_framework\viewsets.py", line 125, in view
    return self.dispatch(request, *args, **kwargs)
  File "C:\Python39\lib\site-packages\rest_framework\views.py", line 509, in dispatch
    response = self.handle_exception(exc)
  File "C:\Python39\lib\site-packages\rest_framework\views.py", line 469, in handle_exception
    self.raise_uncaught_exception(exc)
  File "C:\Python39\lib\site-packages\rest_framework\views.py", line 480, in raise_uncaught_exception
    raise exc
  File "C:\Python39\lib\site-packages\rest_framework\views.py", line 506, in dispatch
    response = handler(request, *args, **kwargs)
  File "C:\Python39\lib\site-packages\rest_framework\mixins.py", line 46, in list
    return Response(serializer.data)
  File "C:\Python39\lib\site-packages\rest_framework\serializers.py", line 745, in data
    ret = super().data
  File "C:\Python39\lib\site-packages\rest_framework\serializers.py", line 246, in data
    self._data = self.to_representation(self.instance)
  File "C:\Python39\lib\site-packages\rest_framework\serializers.py", line 663, in to_representation
    return [
  File "C:\Python39\lib\site-packages\rest_framework\serializers.py", line 664, in <listcomp>
    self.child.to_representation(item) for item in iterable
  File "C:\Python39\lib\site-packages\rest_framework\serializers.py", line 515, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "C:\Python39\lib\site-packages\rest_framework\serializers.py", line 663, in to_representation
    return [

Exception Type: TypeError at /bankdetailapi/
Exception Value: 'Banks' object is not iterable

我还确保我没有打错字。我在堆栈上找到的大多数解决方案都是用 .get_queryset 或 .filter 替换 .all() 方法，这对我不起作用。 我在 admin.py 中注册了我的模型，它通过 admin 可见

Answer 1

删除序列化程序中的many=True。 ForeignKey 链接到单个 Banks 实例，因此并不多。

class BranchSerializer(serializers.ModelSerializer):
    bank = BankSerializer(read_only=True)
    class Meta:
        model = Branches
        fields= ['ifsc','bank','branch','address','city','district','state']
        extra_kwargs = {
                    'bank': {'allow_null': True, 'required': False},   
        }

Answer 2

问题出在BankSerializer，它试图获取所有引用Branch 实例的银行：

bank = BankSerializer(many=True,read_only=True)

您的Branch 模型具有对Banks 的FK 引用，因此只能有一个。如果您删除many=true，您可以修复错误：

bank = BankSerializer(read_only=True)