Django: method of model from querying a different one - django

Question

I have a model CartItem that has a ForeignKey to a Product model.
Because from Product model I get the description, image, etc.
However, I want to have a method called sub_total that returns and integer. I use this to calculate total to be paid for this CartItem.
This sub_total method query a different model costo_de_los_productos using some of the properties of CartItem. like: self.product.category.name, self.product.name, self.size, self.quantity.
I need to return an Integer from sub_total method.
However, something is not right with me query, if I comment it and return 0 it works, but total is 0.
def sub_total(self):
product_price = costo_de_los_productos.objects.filter(category=self.product.category.name,
product = self.product.name,
size=self.size,
quantity=self.quantity).values_list("price", flat=True)
What could be wrong?
class CartItem(models.Model):
cart = models.ForeignKey(Cart, on_delete=models.CASCADE)
product = models.ForeignKey(Product, on_delete=models.CASCADE)
size = models.CharField(max_length=20, choices=TAMANIOS)
quantity = models.CharField(max_length=20, choices=CANTIDADES)
file = models.FileField(upload_to='files', blank=True, null=True)
comment = models.CharField(max_length=100, blank=True, null=True, default='')
uploaded_at = models.DateTimeField(auto_now_add=True)
step_two_complete = models.BooleanField(default=False)
# def __str__(self):
# return str(self.id) + " - " + str(self.size) + " por " + str(self.quantity)
def sub_total(self):
product_price = costo_de_los_productos.objects.filter(category = self.product.category.name,
product = self.product.name,
size=self.size,
quantity=self.quantity).values_list("price", flat=True)
# print(type(product_price))
return product_price
costo_de_los_productos model:
class costo_de_los_productos(models.Model):
category = models.ForeignKey(Category, on_delete=models.CASCADE)
product = models.ForeignKey(Product, on_delete=models.CASCADE)
price = models.IntegerField(default=30)
size = models.CharField(max_length=20, choices=TAMANIOS)
quantity = models.CharField(max_length=20, choices=CANTIDADES)
product model:
class Product(models.Model):
name = models.CharField(max_length=250, unique=False)
slug = models.SlugField(max_length=250, unique=False)
description = models.TextField(blank=True)
category = models.ForeignKey(Category, on_delete=models.CASCADE)
image = models.ImageField(upload_to='product', blank=True, null=True)
available = models.BooleanField(default=True)
created = models.DateTimeField(auto_now_add=True)
updated = models.DateTimeField(auto_now=True)
class Meta:
ordering = ('name',)
verbose_name = 'product'
verbose_name_plural = 'products'
def get_url(self):
return reverse('shop:ProdDetail', args=[self.category.slug, self.slug])
def __str__(self):
return '{}'.format(self.name)
category model:
class Category(models.Model):
name = models.CharField(max_length=250, unique=True)
slug = models.SlugField(max_length=250, unique=True)
description = models.TextField(blank=True, null=True)
image = models.ImageField(upload_to='category', blank=True, null=True)
video = EmbedVideoField(null=True, blank=True)
class Meta:
ordering = ('name',)
verbose_name = 'category'
verbose_name_plural = 'categories'
def get_url(self):
return reverse('shop:allCat', args=[self.slug])
def __str__(self):
return '{}'.format(self.name)
Image of "costo_de_los_productos" from Admin Panel:
UPDATE 1
Cannot print anything after the product_price query.
def sub_total(self):
print("Enters Subtotal")
print(self.product.category.name)
print(self.product.name)
print(self.size)
print(self.quantity)
product_price = costo_de_los_productos.objects.filter(category=self.product.category.name,
product=self.product.name,
size=self.size,
quantity=self.quantity).values_list("price", flat=True)[0]
print("Line after product_price query")
print(type(product_price))
return product_price
Hard coding the values doesn't return expected integer:
def sub_total(self):
print("Enters Subtotal")
print(self.product.category.name)
print(self.product.name)
print(self.size)
print(self.quantity)
product_price = costo_de_los_productos.objects.filter(category="Stickers",
product="Stickers transparentes",
size="5cm x 5cm",
quantity=300).values_list("price", flat=True)[0]
print("Line after product_price query")
print(type(product_price))
return product_price
prints results:
Enters Subtotal
Stickers
Stickers transparentes
5cm x 5cm
300