Inverse of OneToOneField

[lpil]

Hello!

What should be used as the inverse of an OneToOneField?

I've been attempting something like the ForeignKey example but I've not been able to determine what exactly so far. https://github.com/sbdchd/django-types#foreignkey-ids-and-related-names-as-properties-in-orm-models

Thanks, Louis

[sbdchd]

Yeah don't really have any docs on those, but I think it would be similar to the ForeignKey where we have to do some if TYPE_CHECKING stuff

Using the django docs https://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.OneToOneField,

from django.conf import settings
from django.db import models

class MySpecialUser(models.Model):
    user = models.OneToOneField(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
    )
    supervisor = models.OneToOneField(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name='supervisor_of',
    )

And docs say:

>>> user = User.objects.get(pk=1)
>>> hasattr(user, 'myspecialuser')
True
>>> hasattr(user, 'supervisor_of')
True

So we'd need to update User to have the properties, something like:

class User(models.Model):
    # some fields
    if TYPE_CHECKING:
        myspecialuser: MySpecialUser
        user: MySpecialUser

I think the if TYPE_CHECKING might not be necessary, so maybe:

class User(models.Model):
    # some fields
    myspecialuser: MySpecialUser
    user: MySpecialUser

[lpil]

Oh thank you! I thought that the model class would need to be wrapped in some other object. Clearly I've been overthinking this.

I'll try this out and if I can't find any problems perhaps I could add this to the README?

[last-partizan]

The problem with reverse OneToOneField, is it does not exists and will raise RelatedObjectDoesNotExist when there is not corresponding model.

> user = User.objects.get(pk=1)
> hasattr(user, 'myspecialuser')
False
> MySpecialUser.objects.create(user=user)
> hasattr(user, 'myspecialuser')
True

Any ideas how to type this?

[sbdchd]

Yikes, that's pretty dynamic. I'm not sure there is a good way. I think the best we can do is pretend the attr is always there.

[last-partizan]

This could lead to some unexpected errors.

But that's not something type checking should solve. I think it's better to define something like get_mysecialuser which would handle those exceptions.