我做了一个电子商务网站，我想存储在一个整数数组字段购物车元素.我使用PostgreSQL作为我的数据库.我已经通过扩展Django用户模型为购物车创建模型.这里是我的模型

class UserCart(models.Model):
    user=models.OneToOneField(User,on_delete=models.CASCADE)
    user_product=models.IntegerField(blank=True, null=True)
    cart_products = ArrayField(
        models.IntegerField(blank=True),
        default = list
    )

User.profile = property(lambda u:UserCart.objects.get_or_create(user=u)[0])

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下面是我的Form.py。我只从django创建了基本表单。从.models导入UserCart从django.db导入模型从django。contrib.postgres.fields导入ArrayField

class UserCartForm (forms.ModelForm):

    class Meta:
        model= UserCart
        fields = ('user_product',)

型
我在互联网上搜索了很多，但无法找到相关的答案。我希望每当用户点击添加到购物车按钮时，product_id就会存储在cart_products数组中。我在某处读到ArrayFields在Django中表现为列表，所以这里是我的views.py

@login_required
def user_cart(request):
    if request.method=='POST':
        form=UserCartForm(request.POST , instance=request.user.profile)
        if form.is_valid():
            post = form.save(commit=False)
            post.cart_products.append(99)
            post.save()
            return HttpResponseRedirect('/user_login/loggedin')
        else:
            HttpResponse("Error")
    else:
        user=request.user
        profile=user.profile
        form= UserCartForm(instance=profile)
        args={}
        args.update(csrf(request))
        args['form']=form
        return render_to_response('cartapi.html' ,args)

型
它给了我错误，

AttributeError at /cart/ac/
 'NoneType' object has no attribute 'append'
 Request Method:    POST
 Request URL:   http://localhost:8000/cart/ac/
 Django Version:    1.11.2
 Exception Type:    AttributeError
 Exception Value:   
 'NoneType' object has no attribute 'append'
 Exception Location:    C:\Users\Muhammad                
 Jawad\AppData\Local\Programs\Python\Python36-32\mysite\cart\views.py in 
 user_cart, line 19
 Python Executable: C:\Users\Muhammad 
 Jawad\AppData\Local\Programs\Python\Python36-32\python.exe

型
如果我以这种方式保存保存cart_products

post.cart_products=99

型
然后抛出这个错误

column "cart_products" is of type int4range but expression is of type integer
 LINE 1: ...er_id" = 1, "user_cart" = 3000, "cart_products" = 99 WHERE "...
                                                         ^
 HINT:  You will need to rewrite or cast the expression.
 Request Method:    POST
 Request URL:   http://localhost:8000/cart/ac/
 Django Version:    1.11.2
 Exception Type:    ProgrammingError
 Exception Value:   
 column "cart_products" is of type int4range but expression is of type integer
 LINE 1: ...er_id" = 1, "user_cart" = 3000, "cart_products" = 99 WHERE "...
                                                         ^
 HINT:  You will need to rewrite or cast the expression.

型
请在这件事上帮助我。总结我的问题：如何获取user_product作为id并将其保存到cart_products中