Django - store.models.Customer.MultipleObjectsReturned: get() вернула более одного клиента - вернула 2"

Я пытаюсь сделать сайт электронной коммерции, где "AnonymousUser" или гостевой пользователь может заказывать и проверять товары, предоставляя свое имя, электронную почту и адрес. Но после нажатия кнопки "Сделать платеж" в моем терминале возникает ошибка, которая гласит "store.models.Customer.MultipleObjectsReturned: get() вернул более одного клиента - он вернул 2!"

Когда я пытаюсь войти в систему и выполнить процесс для аутентифицированного пользователя, ошибка не возникает. Это происходит только с AnonymousUsers.

Вот мой checkout.html:

Вот мой models.py:

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

# Create your models here.

class Customer(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE, null=True, blank=True)
    name = models.CharField(max_length=200, null=True)
    email = models.CharField(max_length=200)

    def __str__(self):
        return self.name

class Product(models.Model):
    name = models.CharField(max_length=200)
    price = models.DecimalField(max_digits=9, decimal_places=2)
    digital = models.BooleanField(default=False, null=True, blank=True)
    image = models.ImageField(null=True, blank=True)

    def __str__(self):
        return self.name

    @property
    def imageURL(self):
        try:
            url = self.image.url 
        except:
            url = ''
        return url

class Order(models.Model):
    customer = models.ForeignKey(Customer, on_delete=models.CASCADE, null=True, blank=True)
    date_ordered = models.DateTimeField(auto_now_add=True)
    complete = models.BooleanField(default=False)
    transaction_id = models.CharField(max_length=20, null=True)

    def __str__(self):
        return str(self.id)

    @property
    def shipping(self):
        shipping = False
        orderitems = self.orderitem_set.all()
        for i in orderitems:
            if i.product.digital == False:
                shipping = True
        return shipping

    @property
    def get_cart_total(self):
        orderitems = self.orderitem_set.all()
        total = sum([item.get_total for item in orderitems])
        return total

    @property
    def get_cart_items(self):
        orderitems = self.orderitem_set.all()
        total = sum([item.quantity for item in orderitems])
        return total

class OrderItem(models.Model):
    product = models.ForeignKey(Product, on_delete=models.SET_NULL, null=True)
    order = models.ForeignKey(Order, on_delete=models.SET_NULL, null=True)
    quantity = models.IntegerField(default=0, null=True, blank=True)
    date_added = models.DateTimeField(auto_now_add=True)

    @property
    def get_total(self):
        total = self.product.price * self.quantity
        return total

class ShippingAddress(models.Model):
    customer = models.ForeignKey(Customer, on_delete=models.SET_NULL, null=True)
    order = models.ForeignKey(Order, on_delete=models.SET_NULL, null=True)
    address = models.CharField(max_length=200, null=False)
    city = models.CharField(max_length=200, null=False)
    state = models.CharField(max_length=200, null=False)
    zip = models.CharField(max_length=200, null=False)
    date_added = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return self.address

Вот мой views.py:

from django.http import JsonResponse
from django.shortcuts import render
from .models import *
import json
import datetime
from .utils import cookieCart, cartData, guestOrder

def store(request): 

    data = cartData(request)
    cartItems = data['cartItems']

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

def cart(request):

    data = cartData(request)
    cartItems = data['cartItems']
    order = data['order']
    items = data['items']

    context = {'items':items, 'order':order, 'cartItems': cartItems}
    return render(request, 'store/cart.html', context)

def checkout(request):
    data = cartData(request)
    cartItems = data['cartItems']
    order = data['order']
    items = data['items']

    context = {'items':items, 'order':order, 'cartItems': cartItems}
    return render(request, 'store/checkout.html', context)

def updateItem(request):
    data = json.loads(request.body)
    productId = data['productId']
    action = data['action']
    print('Action:', action)
    print('Product:', productId)

    customer = request.user.customer
    product = Product.objects.get(id=productId)
    order, created = Order.objects.get_or_create(customer=customer, complete=False)

    orderItem, created = OrderItem.objects.get_or_create(order=order, product=product)

    if action == 'add':
        orderItem.quantity = (orderItem.quantity + 1)
    elif action == 'remove':
        orderItem.quantity = (orderItem.quantity - 1)

    orderItem.save()

    if orderItem.quantity <= 0:
        orderItem.delete()

    return JsonResponse('Item was added', safe=False)

def processOrder(request):
    transaction_id = datetime.datetime.now().timestamp()
    data = json.loads(request.body)

    if request.user.is_authenticated:
        customer = request.user.customer
        order, created = Order.objects.get_or_create(customer=customer, complete=False)

    else:
        customer, order = guestOrder(request, data)

    total = float(data['form']['total'])
    order.transaction_id = transaction_id

    if total == order.get_cart_total:
        order.complete = True
    order.save()

    if order.shipping == True:
        ShippingAddress.objects.create(
            customer=customer,
            order=order,
            address=data['shipping']['address'],
            city=data['shipping']['city'],
            state=data['shipping']['state'],
            zip=data['shipping']['zip'],
        )

    return JsonResponse('Payment complete!', safe=False)

А вот мой utils.py:

import json
from .models import *

def cookieCart(request):
    try:
        cart = json.loads(request.COOKIES['cart'])
    except:
        cart = {}
    
    print('Cart:', cart)
    items = []
    order = {'get_cart_total':0, 'get_cart_items':0, 'shipping': False}
    cartItems = order['get_cart_items']

    for i in cart:
        try:
            cartItems += cart[i]["quantity"]

            product = Product.objects.get(id=i)
            total = (product.price * cart[i]['quantity'])

            order['get_cart_total'] += total
            order['get_cart_items'] += cart[i]['quantity']

            item = {
                'product':{
                    'id':product.id,
                    'name':product.name,
                    'price':product.price,
                    'imageURL':product.imageURL,
                    },
                'quantity': cart[i]['quantity'],
                'get_total': total,
                }
            items.append(item)

            if product.digital == False:
                order['shipping'] = True

        except:
            pass
    return {'cartItems': cartItems, 'order': order, 'items': items}

def cartData(request):
    if request.user.is_authenticated:
        customer = request.user.customer
        order, created = Order.objects.get_or_create(customer=customer, complete=False)
        items = order.orderitem_set.all()
        cartItems = order.get_cart_items

    else:
        cookieData = cookieCart(request)
        cartItems = cookieData['cartItems']
        order = cookieData['order']
        items = cookieData['items']

    return {'cartItems': cartItems, 'order': order, 'items': items}

def guestOrder(request, data):
    print('User is not logged in...')

    print('COOKIES:', request.COOKIES)
    name = data['form']['name']
    email = data['form']['email']

    cookieData = cookieCart(request)
    items = cookieData['items'] 

    customer, created = Customer.objects.get_or_create(
        email=email,
        )
    customer.name = name
    customer.save()

    order = Order.objects.create(
        customer=customer,
        complete=False,
        )

    for item in items:
        product=Product.objects.get(id=item['product']['id'])

        orderItem = OrderItem.objects.create(
            product=product,
            order=order,
            quantity=item['quantity']
            )

    return customer, order

Как я могу избавиться от этой ошибки и позволить гостевым пользователям осуществлять проверку без необходимости создания учетной записи или входа в систему?

customer, created = Customer.objects.get_or_create(
        email=email,
        )