我创建了一个数字产品的电子商务应用程序，并在我的产品模型的个人资料模型中创建了ManyToMany关系。
添加多对多字段后，在我的Profile模型中，它阻碍了我创建新的Profile并给出以下错误消息：-
ValueError: needs to have a value for field "id" before this many-to-many relationship can be used.
这是我的模特
class Profile(models.Model):
date = models.DateTimeField(auto_now_add=True)
name = models.OneToOneField(settings.AUTH_USER_MODEL,on_delete=models.CASCADE)
subscribed_products = models.ManyToManyField(Product,related_name='products_subscribed',blank=True)
class Product_activation(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL,on_delete=models.CASCADE,null=True,blank=True)
product = models.ForeignKey(Product,on_delete=models.CASCADE,related_name='product_activate')
is_active = models.BooleanField(default=False)
@receiver(pre_save, sender=Profile)
def product_activation(sender,instance,*args,**kwargs):
for product in instance.subscribed_products.all():
if Product_activation.objects.filter(User=instance.Name,product=product).exists():
pass
else:
Product_activation.objects.update_or_create(User=instance.Name,product=product,activate=False,deactivate=True)
class Product(models.Model):
title = models.CharField(max_length=32)
price = models.DecimalField(default=10000.00,max_digits=10,decimal_places=2)
class OrderItem(models.Model):
product = models.OneToOneField(Product, on_delete=models.SET_NULL, null=True)
is_ordered = models.BooleanField(default=False)
date_added = models.DateTimeField(auto_now=True)
date_ordered = models.DateTimeField(null=True)
def __str__(self):
return self.product.title
class Order(models.Model):
ref_code = models.CharField(max_length=15)
owner = models.ForeignKey(Profile, on_delete=models.SET_NULL, null=True)
is_ordered = models.BooleanField(default=False)
items = models.ManyToManyField(OrderItem)
date_ordered = models.DateTimeField(auto_now=True)
def get_cart_items(self):
return self.items.all()
def get_cart_total(self):
return self.items.aggregate(total=Sum('product__price'))['total'] or 0
def __str__(self):
return '{0} - {1}'.format(self.owner, self.ref_code)
class Transaction(models.Model):
profile = models.ForeignKey(Profile, on_delete=models.CASCADE)
order_id = models.CharField(max_length=120)
amount = models.DecimalField(max_digits=100, decimal_places=2)
success = models.BooleanField(default=True)
timestamp = models.DateTimeField(auto_now_add=True, auto_now=False)
def __str__(self):
return self.order_id
我已经在views.py中完成了此操作：
def get_user_pending_order(request):
# get order for the correct user
user_profile = get_object_or_404(Profile, Name=request.user)
order = Order.objects.filter(owner=user_profile, is_ordered=False)
if order.exists():
# get the only order in the list of filtered orders
return order[0]
return 0
@login_required()
def update_transaction_records(request):
# get the order being processed
order_to_purchase = get_user_pending_order(request)
# update the placed order
order_to_purchase.is_ordered=True
order_to_purchase.date_ordered=datetime.datetime.now()
order_to_purchase.save()
# get all items in the order - generates a queryset
order_items = order_to_purchase.items.all()
# update order items
order_items.update(is_ordered=True, date_ordered=datetime.datetime.now())
# Add products to user profile
user_profile = get_object_or_404(Profile, Name=request.user)
# get the products from the items
order_products = [item.product for item in order_items]
user_profile.subscribed_products.add(*order_products)
user_profile.save()
# create a transaction
transaction = Transaction(profile=request.user.profile,
order_id=order_to_purchase.id,
amount=order_to_purchase.get_cart_total(),
success=True)
# save the transcation (otherwise doesn't exist)
transaction.save()
return redirect(reverse('ecommerce_integration:productlist'))
TraceBack：
File "C:\Users\HP\myEnv\lib\site-packages\django\core\handlers\exception.py" in inner
35. response = get_response(request)
File "C:\Users\HP\myEnv\lib\site-packages\django\core\handlers\base.py" in _get_response
128. response = self.process_exception_by_middleware(e, request)
File "C:\Users\HP\myEnv\lib\site-packages\django\core\handlers\base.py" in _get_response
126. response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\contrib\admin\options.py" in wrapper
575. return self.admin_site.admin_view(view)(*args, **kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\utils\decorators.py" in _wrapped_view
142. response = view_func(request, *args, **kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\views\decorators\cache.py" in _wrapped_view_func
44. response = view_func(request, *args, **kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\contrib\admin\sites.py" in inner
223. return view(request, *args, **kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\utils\decorators.py" in _wrapper
62. return bound_func(*args, **kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\views\decorators\debug.py" in sensitive_post_parameters_wrapper
76. return view(request, *args, **kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\utils\decorators.py" in bound_func
58. return func.__get__(self, type(self))(*args2, **kwargs2)
File "C:\Users\HP\myEnv\lib\site-packages\django\utils\decorators.py" in _wrapper
62. return bound_func(*args, **kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\utils\decorators.py" in _wrapped_view
142. response = view_func(request, *args, **kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\utils\decorators.py" in bound_func
58. return func.__get__(self, type(self))(*args2, **kwargs2)
File "C:\Users\HP\myEnv\lib\site-packages\django\contrib\auth\admin.py" in add_view
100. return self._add_view(request, form_url, extra_context)
File "C:\Users\HP\myEnv\lib\site-packages\django\contrib\auth\admin.py" in _add_view
127. return super().add_view(request, form_url, extra_context)
File "C:\Users\HP\myEnv\lib\site-packages\django\contrib\admin\options.py" in add_view
1554. return self.changeform_view(request, None, form_url, extra_context)
File "C:\Users\HP\myEnv\lib\site-packages\django\utils\decorators.py" in _wrapper
62. return bound_func(*args, **kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\utils\decorators.py" in _wrapped_view
142. response = view_func(request, *args, **kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\utils\decorators.py" in bound_func
58. return func.__get__(self, type(self))(*args2, **kwargs2)
File "C:\Users\HP\myEnv\lib\site-packages\django\contrib\admin\options.py" in changeform_view
1451. return self._changeform_view(request, object_id, form_url, extra_context)
File "C:\Users\HP\myEnv\lib\site-packages\django\contrib\admin\options.py" in _changeform_view
1491. self.save_model(request, new_object, form, not add)
File "C:\Users\HP\myEnv\lib\site-packages\django\contrib\admin\options.py" in save_model
1027. obj.save()
File "C:\Users\HP\myEnv\lib\site-packages\django\contrib\auth\base_user.py" in save
73. super().save(*args, **kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\db\models\base.py" in save
729. force_update=force_update, update_fields=update_fields)
File "C:\Users\HP\myEnv\lib\site-packages\django\db\models\base.py" in save_base
769. update_fields=update_fields, raw=raw, using=using,
File "C:\Users\HP\myEnv\lib\site-packages\django\dispatch\dispatcher.py" in send
178. for receiver in self._live_receivers(sender)
File "C:\Users\HP\myEnv\lib\site-packages\django\dispatch\dispatcher.py" in <listcomp>
178. for receiver in self._live_receivers(sender)
File "C:\Users\HP\My Documents\github\erpcloud\erpcloud\userprofile\models.py" in user_created_profilespecific
99. Profile.objects.create(Name=instance,image='userprofile/download (1).jpg')
File "C:\Users\HP\myEnv\lib\site-packages\django\db\models\manager.py" in manager_method
82. return getattr(self.get_queryset(), name)(*args, **kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\db\models\query.py" in create
417. obj.save(force_insert=True, using=self.db)
File "C:\Users\HP\My Documents\github\erpcloud\erpcloud\userprofile\models.py" in save
84. super(Profile, self).save(*args, **kwargs)
File "C:\Users\HP\myEnv\lib\site-packages\django\db\models\base.py" in save
729. force_update=force_update, update_fields=update_fields)
File "C:\Users\HP\myEnv\lib\site-packages\django\db\models\base.py" in save_base
754. update_fields=update_fields,
File "C:\Users\HP\myEnv\lib\site-packages\django\dispatch\dispatcher.py" in send
178. for receiver in self._live_receivers(sender)
File "C:\Users\HP\myEnv\lib\site-packages\django\dispatch\dispatcher.py" in <listcomp>
178. for receiver in self._live_receivers(sender)
File "C:\Users\HP\My Documents\github\erpcloud\erpcloud\userprofile\models.py" in product_activation
105. for product in instance.subscribed_products.all():
File "C:\Users\HP\myEnv\lib\site-packages\django\db\models\fields\related_descriptors.py" in __get__
498. return self.related_manager_cls(instance)
File "C:\Users\HP\myEnv\lib\site-packages\django\db\models\fields\related_descriptors.py" in __init__
795. (instance, self.pk_field_names[self.source_field_name]))
Exception Type: ValueError at /admin/auth/user/add/
Exception Value: "<Profile: surajkar>" needs to have a value for field "id" before this many-to-many relationship can be used.
如果有人知道该解决方案，请提供带有简短说明的正确代码，因为它将帮助我学习新知识。因为我是python和django的新手，所以。
谢谢
答案 0 :(得分：3)
就像错误提示一样，您在保存配置文件之前尝试使用多对多关系。由于m2m关系实际上是一个单独的链接表中的一个条目，在关系的每一侧都存储了对象的ID，因此在该ID实际上存在之前，您不能使用它。即，保存后。
解决方案只是让您的信号监听post_save，而不是pre_save。