Overriding QuerySet.delete() in Django

Question

I have a Django model that holds settings core to the function of an app. You should never delete this model. I'm trying to enforce this application-wide. I've disabled the delete function in the admin, and also disabled the delete method on the model, but QuerySet has it's own delete method. Example:

MyModel.objects.all()[0].delete() # Overridden, does nothing  MyModel.objects.all().delete() # POOF! 

Ironically, the Django docs say has this to say about why delete() is a method on QuerySet and not Manager:

This is a safety mechanism to prevent you from accidentally requesting Entry.objects.delete(), and deleting all the entries.

How having to include .all() is a "safety mechanism" is questionable to say the least. Instead, this effectively creates a backdoor that can't be closed by conventional means (overriding the manager).

Anyone have a clue how to override this method on something as core as QuerySet without monkey-patching the source?

Answer 1

You can override a Manager's default QuerySet by overriding the Manager.get_query_set() method.

Example:

class MyQuerySet(models.query.QuerySet):      def delete(self):         pass  # you can throw an exception   class NoDeleteManager(models.Manager):     def get_query_set(self):         return MyQuerySet(self.model, using=self._db)  class MyModel(models.Model)     field1 = ..     field2 = ..       objects = NoDeleteManager() 

Now, MyModel.objects.all().delete() will do nothing.

For more informations: Modifying initial Manager QuerySets

Answer 2

mixin approach

https://gist.github.com/dnozay/373571d8a276e6b2af1a

use a similar recipe as @manji posted,

class DeactivateQuerySet(models.query.QuerySet):     '''     QuerySet whose delete() does not delete items, but instead marks the     rows as not active, and updates the timestamps     '''     def delete(self):         self.deactivate()      def deactivate(self):         deleted = now()         self.update(active=False, deleted=deleted)      def active(self):         return self.filter(active=True)   class DeactivateManager(models.Manager):     '''     Manager that returns a DeactivateQuerySet,     to prevent object deletion.     '''     def get_query_set(self):         return DeactivateQuerySet(self.model, using=self._db)      def active(self):         return self.get_query_set().active() 

and create a mixin:

class DeactivateMixin(models.Model):     '''     abstract class for models whose rows should not be deleted but     items should be 'deactivated' instead.      note: needs to be the first abstract class for the default objects     manager to be replaced on the subclass.     '''     active = models.BooleanField(default=True, editable=False, db_index=True)     deleted = models.DateTimeField(default=None, editable=False, null=True)     objects = DeactivateManager()      class Meta:         abstract = True 

other interesting stuff

• http://datahackermd.com/2013/django-soft-deletion/
• https://github.com/hearsaycorp/django-livefield