保存扩展用户模型时出现问题。类型对象'UserProfile'没有属性'USERNAME_FIELD'？

Question

我正在尝试通过从Django的内置User模型扩展它来创建模型UserProfile。填写表格后，数据应保存在UserProfile模型中。只是没有发生

最初，数据仅保存在User模型中，而不保存在UserProfile模型中。我从网上申请了一些推荐的解决方案，但现在我什至无法填写表格。在提示注册时，我收到一条错误消息，

类型对象“ UserProfile”没有属性“ USERNAME_FIELD”

#models.py

    from django.db import models
    from django.contrib.auth.models import User

    class UserProfile(models.Model):
        user = models.OneToOneField(User, on_delete=models.CASCADE)
        email = models.EmailField( max_length=254)
        country = models.CharField( max_length=50)



#forms.py
    from django import forms
    from django.contrib.auth.models import User
    from django.contrib.auth.forms import UserCreationForm
    from .models import UserProfile

    class RegistrationForm(UserCreationForm):

        class Meta:
            model = UserProfile
            fields = ['email', 'country']



#views.py
    from django.shortcuts import render,redirect
    from django.http import HttpResponse
    from .forms import RegistrationForm
    from .models import UserProfile 
    from django.contrib.auth.models import User

    def home(request):
         return render(request , 'guide/index.html')

    def register(request):

         if request.method=='POST':
              form = RegistrationForm(request.POST)
              if form.is_valid():
                   u= form.save(commit=False)
                   u.user = request.user
                   u.save()

                   return redirect('home')

         else:
              form=RegistrationForm()          
         return render(request, 'guide/register.html', {'form':form})

我希望代码运行并将数据保存到UserProfile模型，但是页面上说UserProfile没有属性'USERNAME_FIELD'