from django.core.exceptions import ValidationError def check_speaker_event_camp_consistency(sender, instance, **kwargs): if kwargs['action'] == 'pre_add': for pk in kwargs['pk_set']: # check if this event belongs to a different event than the speaker does from program.models import Event event = Event.objects.get(id=pk) if event.camp != instance.camp: raise ValidationError({'events': 'One or more events belong to a different camp (%s) than the speaker (%s) does' % (event.camp, instance.camp)}) def check_speaker_camp_change(sender, instance, **kwargs): for event in instance.events.all(): if event.camp != instance.camp: raise ValidationError({'camp': 'You cannot change the camp a speaker belongs to if the speaker is associated with one or more events.'})