Specify Django proxy model in admin foreign key

Question

In Django 1.11, I have a model Friend , and a proxy model Relative :

class FriendManager(models.Manager):
  def get_queryset(self):
    return super(RelativeManager, self).get_queryset().filter(is_relative=False)

class Friend(models.Model):
  # Model fields defined here
  objects = FriendManager()

class RelativeManager(models.Manager):
  def get_queryset(self):
    return super(RelativeManager, self).get_queryset().filter(is_relative=True)

class Relative(Friend):
  class Meta:
    proxy = True

  objects = RelativeManager()

  def save(self, *args, **kwargs):
    self.is_relative = True
    super(Relative, self).save(*args, **kwargs)

I also have a model FriendPortrait , which has a foreign key field friend :

class FriendPortrait(models.Model):
  friend = models.ForeignKey(Friend)

And a proxy on that:

class RelativePortrait(FriendPortrait):
  class Meta:
    proxy = True

Now, I want the detail view for RelativePortraits to only show relatives in the drop-down for friend .

admin.py:

@admin.register(RelativePortrait)
class RelativePortraitAdmin(admin.ModelAdmin):
  fields = ('friend')

  def formfield_for_foreignkey(self, db_field, request, **kwargs):
    if db_field.name == 'friend':
      kwargs['queryset'] = Relative.objects.all()
    return super(RelativePortraitAdmin, self).formfield_for_foreignkey(db_field, request, **kwargs)

This works, in that only relatives are displayed in the friend drop-down. However, when I try to save a portrait, Django admin gives me a validation error:

friend instance with id 14 does not exist.

How can I specify that I want to use a proxy model for my foreign key in the RelativePortraitAdmin ?

Answer 1

The problem here is that your ForeignKey points to the Friend model. The model's default manager filters out all relatives, so this will not work.

A simple way to solve this would be to restructure your models a bit. Introducing something like a generic Person model and having Friend and Relative inherit from it with proxy=True . The Person model shouldn't have a manager that pre-filters the instances; then you could have your ForeignKey point to person.