model 通过 M2O 关系与 model 链接，通过 M2O 关系进一步与 model 链接引发错误

Question

I am working on an online-shop in django.

I have linked the order model with the cart model through ForeignKey which is further linked with products model through ForeignKey .

models.py :

class products(models.Model):
    image = models.ImageField(upload_to='products/')
    name =  models.CharField(max_length=50)
    slug = models.SlugField(blank=True, unique=True)
    title = models.CharField(max_length=50)
    price = models.FloatField()

    def __str__(self):
        return self.name

class cart(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)         
    item = models.ForeignKey(products, on_delete=models.CASCADE) ###
    slug = models.CharField(max_length=50, default='#')
    quantity = models.IntegerField(default=1)                       
    created_on = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return f'{self.quantity} of {self.item.name}'

    def get_total(self):
        total = self.item.price * self.quantity
        floattotal = float("{0:.2f}".format(total))
        return floattotal

class order(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    item = models.ForeignKey(cart, on_delete=models.CASCADE) ###
    slug = models.SlugField()
    quantity = models.IntegerField()
    created_on = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return f'{self.quantity} of {self.item.item__name}'

I wanted to create object of order as:

def order_view(request, slug):
    cart_qs = cart.objects.filter(user=request.user, slug=slug)
    cart_item = cart_qs[0]
    order.objects.create(user=request.user, item=cart_item.item.name, slug=slug, quantity=cart_item.quantity)  ####

It raises error as:

Cannot assign "'The latest one'": "order.item" must be a "cart" instance.

Why this error arises and how can I resolve this?

Answer 1

You are trying to assign string on Order instance creation where it's expecting a Cart instance. The error raised here:

item=cart_item.item.name

It should be simply:

item=cart_item

, because your model schema expect this:

item = models.ForeignKey(cart, on_delete=models.CASCADE) ###