Automatically create One-To-One relation when using reverse field

Question

When creating two instances of a model and connecting them using a OneToOneField, the connection gets created and saved automatically at object creation:

from django.db import models

class MyModel(models.Model):
    name = models.CharField(primary_key=True, max_length=255)
    next = models.OneToOneField('self', on_delete=models.SET_NULL, related_name='prev', null=True, blank=True)

>>> m2 = MyModel.objects.create(name="2")
>>> m1 = MyModel.objects.create(name="1", next=m2)
>>> m2.prev
<MyModel: 1>
>>> m2.refresh_from_db()
>>> m2.prev
<MyModel: 2>

However, when creating the same connection but using the reverse field, the creation is also done automatically but not the save.

>>> m1 = MyModel.objects.create(name="1")
>>> m2 = MyModel.objects.create(name="2", prev=m1)
>>> m1.next
<MyModel: 2>
>>> m1.refresh_from_db()
>>> m1.next

Note that the last statement doesn't print anything since it returns None

---

How can I have it always save the relation when created using the reverse field without having to manually use .save() each time?

Answer 1

Probably simple way to achieve this could be using pre_save/post_save signal which you see as a viable solution. But not sure how viable this answer would be, try to make some mods and see if this works!

from django.db.models.signals import post_save
from django.dispatch import receiver

class MyModel(models.Model):
    name = models.CharField(primary_key=True, max_length=255)
    next = models.OneToOneField('self', on_delete=models.SET_NULL, related_name='prev', null=True, blank=True)

@receiver(post_save, sender=MyModel)
def mymodel_post_save(sender, instance, **kwargs):
     if hasattr(instance, 'prev'): # if prev exists
          # now check if prev is added next
          if not instance.prev.next: # if next is not present 
                 instance.prev.next = instance
                 MyModel.objects.filter(
                     pk=instance.prev.pk
                 ).update(next=instance)