IntegrityError at /add-to-cart/test2/ NOT NULL constraint failed: core_order.items_id

Question

The problem might be in views.py file in add_to_cart() method. this method is using 3 classes from models.py

Here is my views.py file

from django.shortcuts import render
from .models import Item, Order, OrderItem
from django.views.generic import ListView, DetailView
from django.shortcuts import reverse, get_object_or_404, redirect
from django.utils import timezone


class HomeView(ListView):
    model = Item
    template_name = 'home-page.html'


class ItemView(DetailView):
    model = Item
    template_name = 'product.html'


def checkout(request):
    context = {
        'items': Item.objects.all()
    }
    return render(request, 'checkout-page.html', context)


def add_to_cart(request, slug):
    item = get_object_or_404(Item, slug=slug)
    order_item = OrderItem.objects.create(item=item)
    order_qs = Order.objects.filter(user=request.user, ordered=False)
    if order_qs.exists():
        order = order_qs[0]
        if order.items.filter(item__slug=item.slug).exists():
            order_item.quantity += 1
            order_item.save()
    else:
        ordered_date = timezone.now()
        order = Order.objects.create(
            user=request.user, ordered_date=ordered_date)
        order.items.add(order_item)
        return redirect("core:product",
                        slug=slug)

my models.py file. the Order class id is creating the problem. Exception Value: NOT NULL constraint failed: core_order.items_id Exception Type: IntegrityError

from django.conf import settings
from django.db import models
from django.shortcuts import reverse, get_object_or_404, redirect

Categoty_choice = (
    ('s', 'Shirt'),
    ('sw', 'Sport Wear'),
    ('o', 'Outwear')
)

Label_choice = (
    ('p', 'primary'),
    ('s', 'secondary'),
    ('d', 'danger')
)


class Item(models.Model):
    title = models.CharField(max_length=100)
    price = models.FloatField()
    discount_price = models.FloatField(blank=True, null=True)
    category = models.CharField(choices=Categoty_choice, max_length=2)
    label = models.CharField(choices=Label_choice, max_length=1)
    slug = models.SlugField()
    description = models.TextField()

    def __str__(self):
        return self.title

    def get_absolute_url(self):
        return reverse("core:product", kwargs={"slug": self.slug})

    def get_add_to_cart_url(self):
        return reverse("core:add_to_cart", kwargs={"slug": self.slug})


class OrderItem(models.Model):
    item = models.ForeignKey(Item, on_delete=models.CASCADE)
    quantity = models.IntegerField(default=1)

    def __str__(self):
        return self.item


class Order(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL,
                             on_delete=models.CASCADE)
    items = models.ForeignKey(OrderItem, on_delete=models.CASCADE)
    start_date = models.DateTimeField(auto_now_add=True)
    ordered_date = models.DateTimeField()
    ordered = models.BooleanField(default=False)

    def __str__(self):
        return self.user.username

urls.py file. some patterns ar CBV and some patterns are normal

from django.urls import path
from . import views

app_name = 'core'
urlpatterns = [
    path('', views.HomeView.as_view(), name='home'),
    path('product/<slug>/', views.ItemView.as_view(), name='product'),
    path('add-to-cart/<slug>/', views.add_to_cart, name='add_to_cart'),
    path('checkout/', views.checkout, name='checkout'),

]

Answer 1

You should add more attribute like null = True, blank = True

class OrderItem(models.Model):
    item = models.ForeignKey(Item, on_delete=models.CASCADE, null=True, blank=True)
    quantity = models.IntegerField(default=1)

    def __str__(self):
        return self.item

Answer 2

I was migrating without setting the new field blank = True, null = True. So the existing objects throw out errors because they didn't have any value in the newly added field. So I opened up the manage.py shell and fetched all the objects from that class and individually deleted all objects. Then adding blank = True, null = True to the newly added field, I migrated again. Then added objects again.