Question

I’m developing a system where users will need to match model fields from several models. To assist them, I’ve created an “is_orphan” Boolean field to indicate whether the required relationship (ForeignKey, in this case) should exist but doesn’t yet. It is updated as part of the save routine – example below:

class Caption(models.Model):
    caption = models.TextField()
    is_orphan = models.BooleanField()

    def save(self, *args, **kwargs):
        art_set = self.art_set.all()
        if len(art_set) != 0:
            self.is_orphan = False
        else:
            self.is_orphan = True
        super(Caption, self).save(*args, **kwargs)

My problem is that when I use the admin to release the caption from the other side of the relationship (Art), the change in orphan status for the Caption isn’t reflected unless I go through the Caption save routine. Is there a way to automatically update caption.is_orphan from within the Art model whenever the user changes the caption associated art to a new caption, or no caption at all?

Answer 1

In the save method of Art model:

def save(self, *args, **kwargs):
    old_caption = None
    if self.id:
        old_caption = Art.objects.get(id=self.id).caption
    super(Art, self).save(*args, **kwargs)
    if old_caption and (self.caption != old_caption):
        if old_caption.art_set.all():
            old_caption.is_orphan = False
        else:
            old_caption.is_orphan = True
        old_caption.save()