IndexError: list index out of range

[ammsa]

I have this view:

@method_decorator(login_required, name='dispatch')
class EventCreateView(generic_view.CreateView):
    model = Event
    template_name = 'event/create.html'
    form_class = EventForm
    object = None

    def form_valid(self, form):
        self.object = form.save(commit=False)
        self.object.user = self.request.user
        self.object.save()
        return HttpResponseRedirect(self.get_success_url())

and the following models

class Event(AbstractDateInfo, PolymorphicModel):

    user = models.ForeignKey(User)
    name = models.CharField(max_length=50,
                            blank=False,
                            null=False)
   
class OneToOneEvent(Event):
   ...


class GroupEvent(Event):
   ....

For some reason I was unable to create an Event object. Here is the trace

▶ event/views.py in form_valid
    form_class = EventForm
    object = None
    def form_valid(self, form):
        self.object = form.save(commit=False)
        self.object.user = self.request.user
        self.object.save() ...
        return HttpResponseRedirect(self.get_success_url())
▶ lib/python2.7/site-packages/polymorphic/models.py in save
            self.polymorphic_ctype = ContentType.objects.db_manager(using).get_for_model(self, for_concrete_model=False)
    pre_save_polymorphic.alters_data = True
    def save(self, *args, **kwargs):
        """Overridden model save function which supports the polymorphism
        functionality (through pre_save_polymorphic)."""
        using = kwargs.get('using', self._state.db or DEFAULT_DB_ALIAS)
        self.pre_save_polymorphic(using=using) ...
        return super(PolymorphicModel, self).save(*args, **kwargs)
    save.alters_data = True
    def get_real_instance_class(self):
        """
        Normally not needed.
▶ lib/python2.7/site-packages/polymorphic/models.py in pre_save_polymorphic
        """Normally not needed.
        This function may be called manually in special use-cases. When the object
        is saved for the first time, we store its real class in polymorphic_ctype.
        When the object later is retrieved by PolymorphicQuerySet, it uses this
        field to figure out the real class of this object
        (used by PolymorphicQuerySet._get_real_instances)
        """
        if not self.polymorphic_ctype_id: ...
            self.polymorphic_ctype = ContentType.objects.db_manager(using).get_for_model(self, for_concrete_model=False)
    pre_save_polymorphic.alters_data = True
    def save(self, *args, **kwargs):
        """Overridden model save function which supports the polymorphism
        functionality (through pre_save_polymorphic)."""
▶ lib/python2.7/site-packages/django/db/models/query_utils.py in __get__
        data = instance.__dict__
        if data.get(self.field_name, self) is self:
            # self.field_name is the attname of the field, but only() takes the
            # actual name, so we need to translate it here.
            try:
                f = opts.get_field(self.field_name)
            except FieldDoesNotExist:
                f = [f for f in opts.fields if f.attname == self.field_name][0] ...
            name = f.name
            # Let's see if the field is part of the parent chain. If so we
            # might be able to reuse the already loaded value. Refs #18343.
            val = self._check_parent_chain(instance, name)
            if val is None:
                instance.refresh_from_db(fields=[self.field_name])

Error occurred here:

            f = [f for f in opts.fields if f.attname == self.field_name][0] ...

The cause is probably because I'm inheriting a abstract class AbstractDateInfo, as well as PolymorphicModel. Not sure if it's something allowed to be done using django-polymorphic

[vdboor]

You can try switching the inheritance order, this has helped me fixing another project.

This is something we'd like to fix, but causes rather complex issues within the ORM.