How to send error message to the Django generic DeleteView Confirmation Page using JsonResponse

Question

I am trying to use Django generic DeleteView using the confirmation page. The setup is working as intended.

Later the business logic was changed to prevent deletion if there are child instances assigned to the object being deleted, using on_delete=models.PROTECT in the model.

And the DeleteView has been modified to the following:

class TerritoryDeleteView(LoginRequiredMixin, DeleteView):
    template_name = ".../trty_delete.html"
    model = Territory
    success_url = reverse_lazy('territories_list')

    # THE FOLLOWING MODIFICATION DONE:
    def delete(self, request, *args, **kwargs):
        self.object = self.get_object()
        try:
            self.object.delete()
            return HttpResponseRedirect(success_url)
        except ProtectedError:
            error_message = "This object can't be deleted, as an Outlet is already assigned to the Territory..."
            return JsonResponse(error_message, safe=False)

The above (modified) view works fine. However, in case it encounters the ProtectedError, the error_message is shown in a blank browser page.

How could I display the error_message in the confirmation page (template) itself?

Answer 1

First, change your delete(...) method to catch the ProtectedError error (which you have already done) and then pass the error message as context data to the template as

class TerritoryDeleteView(LoginRequiredMixin, DeleteView):
    template_name = ".../trty_delete.html"
    model = Territory
    success_url = reverse_lazy('territories_list')

    def delete(self, request, *args, **kwargs):
        try:
            return super().delete(request, *args, **kwargs)
        except ProtectedError:
            self.object = self.get_object()
            context = self.get_context_data(
                object=self.object,
                error="Any error msg"
            )
            return self.render_to_response(context)

But, this is not enough, we have to update the template file too.

<form method="post">{% csrf_token %}
    {% if error %}
        {{ error }}
    {% else %}
        <p>Are you sure you want to delete "{{ object }}"?</p>
        <input type="submit" value="Confirm">
    {% endif %}

</form>

Note: This may not fit exactly in your case, but, probably this will give you an idea of how to manage the error message nicely.