Django List objects that will be deleted by deleting the current object

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In my DeleteView template, I'd like to warn the user that deleting the current object will delete the following objects (since the db schema requires on_delete = models.CASCADE).

Here is an example model:

class Book(models.Model):
    course = models.ForeignKey(Course, related_name = 'course_books', on_delete = models.CASCADE, null = True, blank = True)

class Exercise(models.Model):
    book = models.ForeignKey(Book, related_name = 'exercises', on_delete = models.CASCADE, null = True, blank = True)
    ...

class Solution(models.Model):
    exercise = models.ForeignKey(Exercise, related_name = 'solutions', on_delete = models.CASCADE, null = True, blank = True)

So, say the user wants to delete a course, I'd like to warn the user which books, exercises, and solutions will be deleted upon deleting the current book. Something to this effect:

WARNING: Deleting course Programming 101 will delete Python Programming for Beginners and Python By Example.  It will also delete Excersises 1-5 and solutions 1-10

This will require that I can look at the related field to see if the on_delete is set to CASCADE or not. If it is, I should add it to the list of to_be_deleted objects.

I have looked to see if I can check the on_delete attribute of the field:

for related_object in the_course._meta.related_objects:
    dir(related_object.field)

But nothing shows up to help so I'm reaching out here...

django-models django
2 Answers

You can do so doing 

from django.contrib.admin.utils import NestedObjects
from django.db import DEFAULT_DB_ALIAS

collector = NestedObjects(using=DEFAULT_DB_ALIAS)
collector.collect([obj])
print(collector.nested())
user_56815650

You can filter the objects with that particular object_id. For example:

qs = Solution.objects.filter(exercise__book__course_id=course_id).select_related('exercise__book')

This will give a queryset of all the objects of Solution with related foreign key objects exercise and book. Then you can loop through this queryset and check instance._meta.app_label to differentiate between the objects.

user_76658050
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