[FIXED] What is the django-method of fetching the instance in a OneToOneField, accesed from a ManyToManyRelatedManager?

Issue

I was wondering what is the most django correct way of fetching the instance in an OneToOneField, when the instance I'm fetching from is accessed through a ManyToManyRelatedManager?

Specifically, I have a CustomGroup model that has a OneToOneField to auth.Group. Then I want to fetch each CustomGroup instance from the user instance, through the groups manager.

These are my models:

from django.contrib.auth.models import AbstractUser, Group
from django.db import models

class CustomGroup(models.Model):
    group = models.OneToOneField(Group, on_delete=models.CASCADE, related_name="custom_group")


class CustomUser(AbstractUser):
    # my custom fields

I would like to have a get_custom_groups method on the CustomUser model that returns a RelatedManager with the base queryset as all the CustomGroup that this user is related to (much like user.groups, but only with CustomGroup as the model).

What I have usually done is something like this:

def get_custom_groups(self):
    custom_group_ids = self.groups.all().values_list("custom_group", flat=True)
    return CustromGroup.objects.filter(id__in=custom_group_ids)

Is this the best way of doing this, or is there another, smarter way?

Solution

Is this the best way of doing this, or is there another, smarter way?

No, there is no need to first fetch the custom_group items, etc. We can filter directly with:

def get_custom_groups(self):
    return CustromGroup.objects.filter(group__user=self)

Answered By - willeM_ Van Onsem