Ростислав Григорьев

from django.conf import settings
from django.conf.urls.static import static

urlpatterns = [
    # ... the rest of your URLconf goes here ...
] + static(settings.MEDIA_URL, document_root=settings.MEDIA_ROOT)

def application_detail(request, pk):
    application = get_object_or_404(Application, pk=pk)
    return render(request, 'helpdesk/application_detail.html', {'application': application})

<li>Исполнитель(и): {% for executor in application.executor_set.all %}{{ executor.owner.get_full_name }}{% if not forloop.last %}, {%endif %}{% endfor %}

aueryset = Message.objects.all().order_by('-created_at')

class ImagesForSliderSerializer(serializers.ModelSerializer):

    class Meta:
        model = ImagesForSlider
        fields = ('id', 'image', 'image_name')

class GroupSerializer(serializers.ModelSerializer):
    images_for_slider = ImagesForSliderSerializer(many=True)
    
    class Meta:
        model = Group
        fields = (
            # ...
            'images_for_slider',
        )

class AdvertDetailView(DetailView):
    model = Advert
    template_name = "advert/_detail.html"
    context_object_name = "advert"

    def get_context_data(self, **kwargs):
         context = super().get_context_data(**kwargs)
         advert_fields = []
         for field in self.model._meta.fields:
             advert_fields.append((field.verbose_name, str(getattr(self.object, field.name))))
         context['advert_fields'] = advert_fields
         return context

<ul>
{% for verbose_name, value in advert_fields %}
    <li>{{ verbose_name }} -> {{ value }}</li>
{% endfor %}
</ul>

1. _band_form = BandForm(request.POST, instance=user) - здесь задается instance модели User, а нужен Band.
   
2. Если инстанса Band еще нет, его не нужно передавать
   
3. В мета у формы BandForm для fields не указано поле user, значит сохраняться оно не будет даже если передать такой параметр.
   
4. user = User()- несохраненный инстанс юзера бесполезно указывать как ForeignKey для Band. Необходимо его самого сначала сохранить