Django add User and Listing model to a Watchlist model - django

Question

I'm trying to add a Listing model for an eCommerce app to a Wishlist model, but I'm not quite sure where I'm going wrong.
I referenced this post in order to create a Wishlist model and link it to my User and Listing models via a Foreign key for each.
Wishlist post
urls.py
from django.urls import path
from . import views
app_name = "auctions"
urlpatterns = [
# Listing paths
path("", views.index, name="index"),
path("login/", views.login_view, name="login"),
path("logout/", views.logout_view, name="logout"),
path("register/", views.register, name="register"),
path("addlisting/", views.add_listing, name="add_listing"),
path("viewlisting/<int:listing_id>", views.view_listing, name="view_listing"),
# Watchlist paths
path("watchlist_add/<int:listing_id>", views.watchlist_add, name="watchlist_add"),
]
models.py
from django.contrib.auth.models import AbstractUser
from django.db import models
from datetime import datetime
# Categories
categories = [
('misc', 'misc'),
('computers','computers'),
('toys','toys'),
('pets','pets'),
('beauty','beauty'),
('video games','video games'),
('food','food'),
('clothing','clothing'),
]
ACTIVE_CHOICES = [
('Yes', 'Yes'),
('No', 'No'),
]
class User(AbstractUser):
pass
class Listing(models.Model):
listing_owner = models.ForeignKey(User, on_delete=models.CASCADE, related_name="owner")
listing_title = models.CharField(max_length=100)
listing_description = models.TextField(max_length=1200)
listing_img = models.URLField(null=True, blank=True, max_length=250)
created_on = models.DateTimeField(auto_now=True)
starting_price = models.DecimalField(decimal_places=2, max_digits=10, default=1.00)
# From above categories list
category = models.CharField(max_length=30, choices=categories, default='misc')
# From active or inactive list
active_flag = models.CharField(max_length=10, choices=ACTIVE_CHOICES, default="Yes", verbose_name="active listing")
class Meta:
ordering = ['-created_on']
def __str__(self):
return f"Name: {self.listing_title}, Price: ${self.starting_price}, Posted By: {self.listing_owner}"
class Watchlist(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE, null=True)
item = models.ForeignKey(Listing, on_delete=models.CASCADE, null=True)
def __str__(self):
return f"{self.item}"
views.py
#login_required
def view_listing(request, listing_id):
listing = get_object_or_404(Listing, pk=listing_id)
if request.method == "GET":
return render(request, "auctions/view_listing.html" , { "listing": listing})
else:
try:
form = ListingForm(request.POST, instance=listing)
form.save()
return redirect("auctions:index")
except ValueError:
return render(request, "auctions/view_listing.html", {"listing": listing, "form": form})
#login_required
def watchlist_add(request, listing_id):
listing = get_object_or_404(Listing, pk=listing_id)
obj, created = Watchlist.objects.get_or_create(user=request.user, item_id=listing_id)
return HttpResponseRedirect(reverse("auctions:index"))
view_listing.html
{% extends "auctions/layout.html" %} {% block body %}
<h1 class="display-3 text-center mb-5">{{ listing.listing_title }}</h1>
<div class="container d-flex">
<figure class="figure">
{% if listing.listing_img %}
<img src="{{ listing.listing_img }}" alt="{{ listing.listing_title }}" title="{{ listing.listing_title }}"> {% else %}
<img src="https://res.cloudinary.com/guez/image/upload/v1606759078/cs50_commerce_project/default_image.jpg" alt="default image" title="default image"> {% endif %}
<figcaption class="figure - caption">Listed By: {{ listing.listing_owner|capfirst }}</figcaption>
</figure>
<div class="container m-4">
<p class="display-4">${{ listing.starting_price }}</p>
<hr>
<p class="">Description: {{ listing.listing_description }}</p>
<p class="figure-caption">Category: {{ listing.category|capfirst }}</p>
<small></small>
</div>
<div class="container">
<form action="{% url 'auctions:watchlist_add' listing.pk %}" method="post">
{% csrf_token %}
<input type="hidden" value="{{ listing.pk }}" name="listing">
<input type="submit" value="Add To Watchlist" class="btn btn-outline-warning">
</form>
<!--Add To Watchlist-->
</div>
</div>
{% endblock %}
Before there are any items on my wishlist, I go to view_listing.html and hit the 'Add To Watchlist' button. I then get an AttributeError that reads "AttributeError: 'Listing' object has no attribute 'remove'". Here's the stack trace:
System check identified no issues (0 silenced).
December 07, 2020 - 00:08:42
Django version 3.1, using settings 'commerce.settings'
Starting development server at http://0.0.0.0:8080/
Quit the server with CONTROL-C.
[07/Dec/2020 00:08:44] "GET /admin/auctions/watchlist/2/delete/ HTTP/1.1" 200 5409
[07/Dec/2020 00:08:45] "POST /admin/auctions/watchlist/2/delete/ HTTP/1.1" 302 0
[07/Dec/2020 00:08:45] "GET /admin/auctions/watchlist/ HTTP/1.1" 200 5215
[07/Dec/2020 00:08:46] "GET /admin/jsi18n/ HTTP/1.1" 200 3187
[07/Dec/2020 00:08:48] "GET /admin/auctions/watchlist/ HTTP/1.1" 200 5215
[07/Dec/2020 00:08:48] "GET /admin/jsi18n/ HTTP/1.1" 200 3187
[07/Dec/2020 00:08:51] "GET /admin/auctions/watchlist/ HTTP/1.1" 200 5215
[07/Dec/2020 00:08:51] "GET /admin/jsi18n/ HTTP/1.1" 200 3187
[07/Dec/2020 00:09:01] "GET / HTTP/1.1" 200 3962
[07/Dec/2020 00:09:03] "GET /viewlisting/8 HTTP/1.1" 200 2350
Name: Sega Genesis, Price: $1.00, Posted By: guez already in cart.
Internal Server Error: /watchlist_add/8
Traceback (most recent call last):
File "/home/ubuntu/.local/lib/python3.7/site-packages/django/core/handlers/exception.py", line 47, in inner
response = get_response(request)
File "/home/ubuntu/.local/lib/python3.7/site-packages/django/core/handlers/base.py", line 179, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/home/ubuntu/.local/lib/python3.7/site-packages/django/contrib/auth/decorators.py", line 21, in _wrapped_view
return view_func(request, *args, **kwargs)
File "/home/ubuntu/project2/commerce/auctions/views.py", line 108, in watchlist_add
obj.listings.remove(listing)
AttributeError: 'Listing' object has no attribute 'remove'
[07/Dec/2020 00:09:06] "POST /watchlist_add/8 HTTP/1.1" 500 73233
I want to add the item to Wishlist via the watchlist_add function and then pass that new Wishlist object to the view_listing function in order to determine whether the button should or should not exist in the view_listing.html template if the item is already in request.user 's Watchlist.
?

Answer 1

Your code seems having a logic problem. You get_or_create a WatchList object, and you test if that obj is in the WatchList or not. The obj will always be in your WatchList.objects.all(), because it was there before or you just created.
obj.listings.remove(listing)
According to [django doc about remove()][1], you should use it the following way:
obj.listing_set.remove(obj)
together, how about something like:
#login_required
def watchlist_add(request, listing_id):
listing = get_object_or_404(Listing, pk=listing_id)
already_existed = Watchlist.objects.get_or_create(user=request.user, item=listing).exists()
if already_existed:
# do something:
# return ...
else:
Watchlist.objects.create(user=request.user, item=listing)
# do something
# return ....
Or you can still use get_or_create...
#login_required
def watchlist_add(request, listing_id):
listing = get_object_or_404(Listing, pk=listing_id)
obj, created = Watchlist.objects.get_or_create(user=request.user, item_id=listing_id)
if created: # means it was a new one
# do something
# return ...
else:
# do something, maybe delete whatever button you want to delete,
# maybe return a variable like below
# and in template you have {% if delete_button %}
# delete_button = True
# return ....
[1]: https://docs.djangoproject.com/en/3.1/ref/models/relations/#django.db.models.fields.related.RelatedManager.remove