Custom Django model.save() kwarg to avoid executing costly codes if there are lots of formsets in the page.

django-formset--custom-kwarg--formset-save--model-save.py

# forms.py
class EventSessionFormSet();
    ...
    
    def save(self, commit=True):
        sessions = []
        forms = self.forms
        total_forms = len(forms)
        
        for i, form in enumerate(forms):
            update_event_fields = False
            
            # Trigger the save kwargs only if form is the last in formset
            # because the kwarg is used to avoid executing a custom block in EventSession.save()
            # every time a form is saved (performance optimization).
            if i == total_forms - 1:
                update_event_fields = True

            # form.save() and model.save() combo to pass a custom kwarg.
            session = form.save(commit=False)
            session.save(update_event_fields=update_event_fields)
            
            sessions.append(session)
            
        # Need to return the saved instances.
        return sessions

      
# models.py
class EventSession():
    event = models.ForeignKey(Event, related_name='sessions')
    ...

    def save(self, *args, **kwargs):
        update_event_fields = False
         
        # Remove the custom kwarg before calling super() to prevent error.
        if kwargs.has_key('update_event_fields'):
            update_event_fields = kwargs.pop('update_event_fields')

        super(EventSession, self).save(*args, **kwargs)

        if update_event_fields and self.event.has_multi_sessions:
            sessions = self.event.sessions

            if sessions.exists():
                self.event.session_earliest_starts = sessions.order_by('starts').first().starts
                self.event.session_latest_ends = sessions.order_by('ends').last().ends
                self.event.save()