无法使用 Django 和内容类型中的通用外键访问相关对象

Question

hey guys i don't know if what i am doing is right but i have these class or model

class CartItem(models.Model):
    cart = models.ForeignKey(Cart, on_delete=models.CASCADE)
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.UUIDField()
    content_object = GenericForeignKey('content_type','object_id')

and i have this related model using the generic foreign key

class MstProduct(PhysicalProduct):
    user = models.ForeignKey(User, models.PROTECT)
    purposes = models.ManyToManyField(ProductPurpose, null = True, blank = True, related_name='products')
    madeOf = models.ManyToManyField(AffeliateProduct, null = True, blank = True)
    category = models.ForeignKey(Category, on_delete=models.PROTECT, related_name = "physical_products")
    theme = models.ForeignKey(Theme, on_delete= models.SET_NULL, null = True, blank = True, related_name = 'physical_products')
    art_type = models.ForeignKey(ArtType, on_delete=models.SET_NULL, null = True,blank = True)
    cart_items = GenericRelation(CartItem,related_query_name='product')

what i wanna do is to access the product related to CartItem instance from the generic foreign key field, i tried to do it using the related_query_name argument but after trying this:

CartItem.objects.first().product

I get an error like this:

Traceback (most recent call last):
  File "/home/alaa/.local/lib/python3.10/site-packages/django/db/models/fields/related_descriptors.py", line 678, in get_queryset
    return self.instance._prefetched_objects_cache[
AttributeError: 'CartItem' object has no attribute '_prefetched_objects_cache'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/alaa/.local/lib/python3.10/site-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/alaa/.local/lib/python3.10/site-packages/django/db/models/fields/related_descriptors.py", line 683, in get_queryset
    return self._apply_rel_filters(queryset)
  File "/home/alaa/.local/lib/python3.10/site-packages/django/db/models/fields/related_descriptors.py", line 640, in _apply_rel_filters
    val = getattr(self.instance, field.attname)
AttributeError: 'CartItem' object has no attribute 'productId'

productId is basically a field of this abstract class:

class Product(models.Model):
    productId = models.UUIDField(default=uuid4, primary_key=True, editable=False)
    picture = models.ImageField()
    discription = models.TextField(max_length=2000)
    price = models.FloatField()
    orders = GenericRelation(Order, related_query_name='orders')
    createdAt = models.DateTimeField(auto_now_add=True)
    updatedAt = models.DateTimeField(auto_now=True)
    rates = GenericRelation(ProductRate,related_query_name='rates')
    themes = GenericRelation(Theme)
    purchase_num = models.PositiveBigIntegerField()

I am confused a bit here, if anyone can help i would really appreciate it

Answer 1

According to the docs , try.

obj_cartitem = obj_product.productId