Using a Non-Default Manager with GenericForeignKey()

Question

I have altered the default manager on some of the objects which a GenericForeignKey() can reference such that those objects may no longer appear within that default manager.

I have other managers which will be able to find these deleted objects, but I see no way to tell the content types framework about them. Is this possible?

I am implementing 'soft deletion' with some models which involves the following managers:

from django.db import models

SDManager(models.Manager):

    def get_query_set(self):
        return super(SDManager, self).get_query_set().filter(is_deleted=False)

SDDeletedManager(models.Manager):

    def get_query_set(self):
        return super(SDDeletedManager, self).get_query_set().filter(is_deleted=True)

This allows me to do the following:

SDModel(models.Model):
    # ...
    objects = SDManager() # Only non (soft) deleted objects
    all_objects = models.Manager() # The default manager
    deleted_objects = SDDeletedManager() # Only (soft) deleted objects

When using a GenericForeignKey() field in a model to reference an object defined such as SDModel, it uses the _default_manager attribute which evaluates to the objects manager, to get the reference. This means it looses references when objects are soft deleted.

This was one of the main reasons I was using GenericForeignKey() fields. A solution I have been milling over is implementing a lesser version of the content types framework, so that I can define my own get_object() which uses the all_objects manager to access the references object.

So my question really is:

Is it possible to use a non-default manager with the existing content types framework so that it finds the soft deleted objects, or will I have to re implement all the parts I need from scratch?

Answer 1

I have the exact same issue as you, and after diving into the documentation/source it looks like Django does not provide an out of the box way to do this. The simplest method I found was to subclass GenericForeignKey and then override the __get__ method.

The troublesome line is where it calls:

rel_obj = ct.get_object_for_this_type(pk=getattr(instance, self.fk_field))

So this line needs to be rewritten as:

rel_obj = ct.model_class().all_objects.get(pk=getattr(instance, self.fk_field))

It's a little bit hackish but it works, and you then get to use the full power of GenericForeignKey like you usually would.