Modify related object before creating it

Using Django The Admin
1

I have quite some experience with Python and SQL, but am quite new to Django. I’m currently exploring the possibilities of the admin interface. On the admin page of a parent object I have this TabularInline:

class ScheduleEntryInline(admin.TabularInline):
    def __init__(self, day, *args, **kwargs):
        self.day = day
        super().__init__(*args, **kwargs)

    def get_queryset(self, request):
        qs = super().get_queryset(request)
        return qs.filter(day=self.day)

In the parents ModelAdmin I override get_formsets_with_inlines to dynamically add multiple of those instances for various days. The forms are displayed as expected and work fine until I try to save my changes.

The day field of the newly created ScheduleEntry objects need to be set. My first try was to override save_model but that seems to be called only for the parent object. Next I found save_related which is called, but does not yet receive the objects themselves.

It would probably be possible create the objects from the form information passed to save_related but then I will probably have to handle more save-related code, which will make my code brittle against future changes.

I wonder whether there is a better option to modify the related objects before creating them?

2

The following override kind of works. It is obviously not the most efficient and elegant solution, but the code is not executed very often:

def save_related(self, request, form, formsets, change):
    form.save_m2m()
    for formset in formsets:
        for item in formset.save():
            if isinstance(item, ScheduleEntry) and item.day == None:
                item.day = formset.day
                item.save()

I’m still open for suggestions how to handle this in a smarter way.