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