Django cannot save to to second database

Question

I've tried using multiple database in my Django project. I create a model with foreign key to User but it can't save to second database.

This is the UserData model:

class UserData(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE, related_name='user', related_query_name='user')
    is_controller = models.BooleanField(default=False)
    phone_number = models.CharField(max_length=255, blank=True, null=True)

Then in views:

instance = UserData(
    user=request.user,
    nim=nim,
    phone_number=phone
)

After that, I save the instance:

>>> instance.save() #it works on default database (sqlite)
>>> instance.save(using='db_alias') # return an error

The error said it was cannot add or update child row because of the foreign key

(1452, 'Cannot add or update a child row: a foreign key constraint fails ('labs'.'presence_userdata', CONSTRAINT 'presence_userdata_user_id_4b3dfc56_fk_auth_user_id' FOREIGN KEY ('user_id') REFERENCES 'auth_user' ('id'))')`

Can anyone help me solve this problem?

Answer 1

Django does not support any FK or M2M relations between multiple databases. As stated in the documentation, any FK or M2M relation must happen in a single database instance.

Reference https://docs.djangoproject.com/en/4.1/topics/db/multi-db/#cross-database-relations