尝试在视图中设置会话值时，为什么会出现 TypeError（Object ... is not JSON serializable）？

Question

当我尝试在视图中（在 basket 应用程序中）设置会话值时，出现了这个奇怪的 TypeError：“产品类型的对象不是 JSON 可序列化的”。错误发生在 request.session['Hello'] = 'foo'。

不过，这个错误不会发生在其他地方。例如，在 store 应用程序中，在 views.py 中，以下 request.session['Hello World'] = 'Alloy' 效果很好。

为什么会这样？

篮子应用程序/views.py

from django.shortcuts import render, get_object_or_404
from django.http import JsonResponse

from . basket import Basket
from store.models import Product
from discount.forms import UserDiscountForm


def basket_summary(request):
    basket = Basket(request)
    context = {'basket':basket}
    request.session['Hello'] = 'foo'
    return render(request,"store/basket_summary.html",context)


def basket_add(request):
    basket = Basket(request)

    if request.POST.get('action') == 'post':
        product_id = int(request.POST.get('productid'))
        product_qty = int(request.POST.get('productqty'))
        product = get_object_or_404(Product, id=product_id)
        basket.add(product=product, qty=product_qty)
        basketqty = basket.__len__()
        response = JsonResponse({'qty':basketqty})
        return response


def basket_add_new(request):
    basket = Basket(request)

    if request.POST.get('action') == 'post':
        product_id = int(request.POST.get('productid'))
        product = get_object_or_404(Product, id=product_id)
        basket.add_new(product=product)
        basketqty = basket.__len__()
        response = JsonResponse({'qty':basketqty})
        return response


def basket_delete(request):
    basket = Basket(request)

    if request.POST.get('action') == 'post':
        product_id = int(request.POST.get('productid'))
        basket.delete(product=product_id)
        basketqty = basket.__len__()
        baskettotal = basket.get_total_price()
        response = JsonResponse({'qty':basketqty, 'subtotal':baskettotal})
        return response


def basket_update(request):
    basket = Basket(request)

    if request.POST.get('action') == 'update-basket':
        product_id = int(request.POST.get('productid'))
        product_qty = int(request.POST.get('productqty'))
        basket.update(product=product_id, qty=product_qty)
        basketqty = basket.__len__()
        baskettotal = basket.get_total_price()
        itemtotal = basket.get_subtotal_price(product=product_id)
        response = JsonResponse({'qty':basketqty, 'baskettotal':baskettotal, 'product_qty':product_qty, 'itemtotal':itemtotal})
        return response

篮子应用程序/basket.py

from decimal import Decimal

from store.models import Product


class Basket():
    def __init__(self, request):
        self.session = request.session
        basket = self.session.get('cart')

        if 'cart' not in request.session:
            basket = self.session['cart'] = {}

        self.basket = basket


    def save(self):
        self.session.modified = True


    def add(self, product, qty):
        """
        Adding and updating basket session data
        """
        product_id = str(product.id)
        price = float(product.price)
        subtotal = qty * price

        if product_id not in self.basket:
            self.basket[product_id] = {'price': price, 'qty':int(qty), 'subtotal': subtotal}

        else:
            self.basket[product_id]['qty'] = qty
            self.basket[product_id]['subtotal'] = subtotal

        self.save()


    def add_new(self, product):
        """
        Adding new item in basket session data
        """
        product_id = str(product.id)

        if product_id not in self.basket:
            self.basket[product_id] = {'price': float(product.price), 'qty':1, 'subtotal':float(product.price)}
            # self.basket[product_id] = {'price': float(product.price), 'qty':1}

        else:
            pass

        self.save()


    def __iter__(self):
        """
        Collect the product_id in the session data to query the database and return products
        """
        
        product_ids = self.basket.keys()
        products = Product.objects.filter(id__in=product_ids)
        basket = self.basket.copy()

        for product in products:
            basket[str(product.id)]['product'] = product
    
        for item in basket.values():
            item['price'] = float(item['price'])
            item['total_price'] = item['price'] * item['qty']
    
            yield item


    def __len__(self):
        """
        Get the basket data and count the quantity of all items
        """
            
        return sum(item['qty'] for item in self.basket.values())


    def get_total_price(self):

        return sum(float(item['price']) * item['qty'] for item in self.basket.values())


    def get_subtotal_price(self, product):
        product_id = str(product)

        return self.basket[product_id]['qty'] * self.basket[product_id]['price']



    def delete(self, product):
        """
        Delete item from session data
        """
        product_id = str(product)

        if product_id in self.basket:
            del self.basket[product_id]
        
        self.save()


    def update(self, product, qty):
        """
        Update item in session data
        """
        product_id = str(product)
        
        if product_id in self.basket:
            self.basket[product_id]['qty'] = qty
            self.basket[product_id]['subtotal'] = self.basket[product_id]['qty'] * self.basket[product_id]['price']
        
        self.save()


    def clear(self):
        try:
            del self.session['cart']
        except KeyError:
            pass

        self.save()

商店应用程序/models.py

from django.db import models
from django.urls import reverse


class Category(models.Model):
    name = models.CharField(max_length=254, db_index=True)
    slug = models.SlugField(max_length=254, unique = True)


    class Meta:
        verbose_name_plural = 'categories'


    def __str__(self):
        return self.name



class Product(models.Model):
    category = models.ForeignKey(Category, related_name='product', on_delete=models.CASCADE)
    title = models.CharField(max_length=254)
    description = models.TextField(blank=True)
    image = models.ImageField(upload_to='images/', default='images/default.png')
    slug = models.SlugField(max_length=254, unique = True)
    price = models.DecimalField(max_digits=5, decimal_places=2)
    is_active = models.BooleanField(default=True)
    created = models.DateTimeField(auto_now_add=True)
    updated = models.DateTimeField(auto_now=True)
    image2 = models.ImageField(upload_to='images/', null=True, blank=True)
    image3 = models.ImageField(upload_to='images/', null=True, blank=True)
    stock = models.IntegerField()
    weight = models.IntegerField(verbose_name='Poids (g)')


    class Meta:
        verbose_name_plural = 'products'
        ordering = ('-created', ) # ordering in descending order


    def get_absolute_url(self):
        return reverse('store:product_detail', args=[self.slug])


    def __str__(self):
        return self.title

商店应用程序/views.py

from django.shortcuts import get_object_or_404, render
from requests.sessions import session

from .models import Category, Product



def home(request):
    print('----------// HOME PAGE  //----------')
    request.session['Hello World'] = 'Alloy'
    context = {}
    return render(request, 'store/home.html', context)


def categories(request):
    categories = Category.objects.all()
    context = {'categories': categories}
    return render(request, 'store/categories.html', context)


def all_products(request):
    products = Product.objects.all()
    context = {'products': products}
    return render(request, 'store/all_products.html', context)


def product_detail(request, slug):
    product = get_object_or_404(Product, slug=slug, is_active=True)
    context = {'product': product}
    return render(request, 'store/product_details.html', context)

追溯

Environment:


Request Method: GET
Request URL: http://127.0.0.1:8000/basket/

Django Version: 3.2
Python Version: 3.9.4
Installed Applications:
['django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'store',
 'account',
 'basket',
 'orders',
 'payment',
 'contact',
 'address',
 'discount',
 'shipping']
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:\Users\Utilisateur\Documents\Environments\monoi_django_virtualenv\lib\site-packages\django\core\handlers\exception.py", line 47, in inner
    response = get_response(request)
  File "C:\Users\Utilisateur\Documents\Environments\monoi_django_virtualenv\lib\site-packages\django\utils\deprecation.py", line 119, in __call__
    response = self.process_response(request, response)
  File "C:\Users\Utilisateur\Documents\Environments\monoi_django_virtualenv\lib\site-packages\django\contrib\sessions\middleware.py", line 61, in process_response
    request.session.save()
  File "C:\Users\Utilisateur\Documents\Environments\monoi_django_virtualenv\lib\site-packages\django\contrib\sessions\backends\db.py", line 83, in save
    obj = self.create_model_instance(data)
  File "C:\Users\Utilisateur\Documents\Environments\monoi_django_virtualenv\lib\site-packages\django\contrib\sessions\backends\db.py", line 70, in create_model_instance
    session_data=self.encode(data),
  File "C:\Users\Utilisateur\Documents\Environments\monoi_django_virtualenv\lib\site-packages\django\contrib\sessions\backends\base.py", line 114, in encode
    return signing.dumps(
  File "C:\Users\Utilisateur\Documents\Environments\monoi_django_virtualenv\lib\site-packages\django\core\signing.py", line 110, in dumps
    return TimestampSigner(key, salt=salt).sign_object(obj, serializer=serializer, compress=compress)
  File "C:\Users\Utilisateur\Documents\Environments\monoi_django_virtualenv\lib\site-packages\django\core\signing.py", line 172, in sign_object
    data = serializer().dumps(obj)
  File "C:\Users\Utilisateur\Documents\Environments\monoi_django_virtualenv\lib\site-packages\django\core\signing.py", line 87, in dumps
    return json.dumps(obj, separators=(',', ':')).encode('latin-1')
  File "c:\users\utilisateur\appdata\local\programs\python\python39\lib\json\__init__.py", line 234, in dumps
    return cls(
  File "c:\users\utilisateur\appdata\local\programs\python\python39\lib\json\encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "c:\users\utilisateur\appdata\local\programs\python\python39\lib\json\encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "c:\users\utilisateur\appdata\local\programs\python\python39\lib\json\encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '

Exception Type: TypeError at /basket/
Exception Value: Object of type Product is not JSON serializable

Answer 1

问题出在 __iter__ 类的 Basket 方法中。我相信您会遍历模板中的篮子对象，以便在请求中使用它（因为视图中没有循环）。

现在方法有什么问题？那么你有这个特殊的行 basket = self.basket.copy()，它的作用是制作字典的浅拷贝，即引用的内部对象是相同的，但你有一个嵌套的字典，这意味着当您更改嵌套字典时，您实际上更改了篮子中的同一个字典！您可以使用 copy.deepcopy [Python docs] 对字典进行深层复制：

import copy


def __iter__(self):
    ...
    basket = copy.deepcopy(self.basket)
    ...