Using self.object in CreateView to create objects in other tables

Question

When a user makes a new listing using a CreateView, I am trying to use this new object to create a Bid in the Bids table.

class ListingCreateView(CreateView):
    model = Listing 
    fields = ['title', 'description', 'starting_bid', 'url'] 

    def form_valid(self, form):
        form.instance.author = self.request.user
        return super().form_valid(form)
    
    def post(self, request, *args: Any, **kwargs: Any):
        self.object = self.get_object()
        starting_bid = self.request.POST['starting_bid']
        Bids.objects.create(bid_value=starting_bid, bidder=self.request.user, item=self.object)
        return super().post(request, *args, **kwargs)

But it returns the error Generic detail view ListingCreateView must be called with either an object pk or a slug in the URLconf.

The docs say that "When using CreateView you have access to self.object, which is the object being created. If the object hasn’t been created yet, the value will be None."

When using a CreateView, when would self.object contain the object being created? How would I work with the object that has just been created in a CreateView?

Answer 1

You can implement the logic in the .form_valid(…) method ^[Django-doc], for example:

from django.contrib.auth.mixins import LoginRequiredMixin
from django.http import HttpResponseRedirect

class ListingCreateView(LoginRequiredMixin, CreateView):
    model = Listing 
    fields = ['title', 'description', 'starting_bid', 'url'] 

    def form_valid(self, form):
        form.instance.author = self.request.user
        self.object = form.save()
        Bids.objects.create(
            bid_value=form.cleaned_data['starting_bid'],
            bidder=self.request.user,
            item=self.object
        )
        return HttpResponseRedirect(self.get_success_url())

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Note: normally a Django model is given a singular name, so Bid instead of Bids.

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Note: You can limit views to a class-based view to authenticated users with the LoginRequiredMixin mixin ^[Django-doc].