Django Model OneToOneField without creating additional _id database column

Question

I'm working with an Account model and I want to inner join it with a Settings model without having to create an additional settings_id column in my Account model, because the PK on the Account table matches the PK on the settings table exactly. I've been trying to set up a OneToOne relationship between these tables & columns, but can't figure out how to do that without having to create a new column or something. I'm trying to work with the existing schema as much as possible and would prefer to not create unnecessary columns.

Class Account(models.Model):
    login_id = models.AutoField(primary_key=True)
    settings = models.OneToOneField('Settings', to_field='login_id', null=True,
        related_name='settings', db_column='login_id') # Doesn't work because login_id already exists....


Class Settings(model.Model):
    login_id = models.OneToOneField('Account', to_field='login_id', related_name='account')

Basically, the query I'm trying to replicate is:

SELECT * FROM account
INNER JOIN settings
ON account.login_id=settings.login_id
WHERE account.login_id=1

Based on the errors, Django's ORM seems really persistent on creating a new column in the Account table, but I don't see the point of adding a new column when the relationship between the 2 tables is so simple: account.login_id = settings.login_id

Answer 1

Although I've never tried it myself, declaring the OneToOneField as the primary key should work.

class Account(models.Model):
    login_id = models.AutoField(primary_key=True)

class Settings(model.Model):
    account = models.OneToOneField('Account', to_field='login_id', 
        primary_key=True, related_name='settings')

Declaring the primary_key will keep Django from trying to create a primary key column for you, and with this setup you can access account.settings and settings.account or settings.account_id.

Answer 2

Here's what I ended up doing:

class Account(models.Model):
    login_id = models.AutoField(primary_key=True)

    def get_settings_dict(self):
        try:
            return self.settings.to_dict()
        except Settings.DoesNotExist:
            return Settings.get_defaults_dict()

class Settings(model.Model):
    account = models.OneToOneField('Account', to_field='login_id', related_name='settings')
    # other settings properties
    # other settings properties

    def to_dict(self):
        # return current values as dict

    @staticmethod
    def get_defaults_dict():
        # return default values dict

This allowed me to access a user's settings via account.settings without having to create an additional settings_id column on the Account model. The OneToOne relationship wasn't needed on both models.

Also, the get_settings_dict method returns the default settings when the settings do not exist yet for a user. This is a nice convenience that prevents me from having to do a null check every time I access the user's settings via account.settings.