How to use decimal quantity for Django-Shop CartItems

Question

Hi I'm trying to edit the demo of Django-Shop.

I installed the version 1.2.4 of Django-Shop and Django 3.0.14 using Python 3.7.5.

In my case, I want to sell Products also by weight. As said in the documentation, I have to rewrite the CartItem.

from django.db import models
from django.utils.translation import ugettext_lazy as _

from shop.models import cart


class CartItem(cart.BaseCartItem):
    quantity = models.DecimalField(_("Cart item quantity"), decimal_places=3, max_digits=3)

I imported this CartItem in my models.py. After that, I had to rewrite the quantity in the class OrderItem as well.

class OrderItem(BaseOrderItem):
    quantity = models.DecimalField(_("Ordered quantity"), decimal_places=3, max_digits=3)
    # quantity = models.PositiveIntegerField(_("Ordered quantity"))
    canceled = models.BooleanField(_("Item canceled "), default=False)

    def populate_from_cart_item(self, cart_item, request):
        super().populate_from_cart_item(cart_item, request)
        # the product's unit_price must be fetched from the product's variant
        try:
            variant = cart_item.product.get_product_variant(
                product_code=cart_item.product_code)
            self._unit_price = Decimal(variant.unit_price)
        except (KeyError, ObjectDoesNotExist) as e:
            raise CartItem.DoesNotExist(e)

Now I can run the server without problems, but I can't add something to my cart.

I don't know what to do...

Answer 1

If the models.DecimalField are exchanged for models.FloatField, the products can be added to the shopping cart as expected. Apparently the documentation in which the DecimalField is explicitly mentioned is wrong.