Restricting User to have one one-to-one relationship with any one of the given models Django

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I am having two model classes named as Leader and Member, both have a OnetoOne relationship with User, as you can see below:

from django.db import models
from django.contrib.auth.models import User

class Profile(models.Model):
    user = models.OneToOneField(User, on_delete=models.DO_NOTHING)
    # Abstract model class for common fields in Leader and Member
    class Meta:
        abstract = True

class Leader(Profile):
    # attributes

    # def save(self) -> None:
    #     if Member.objects.filter(user=self.user).first() == None:
    #         return super().save()
    #     else:
    #         raise ValidationError("User is already a member, migrate it to make it leader.")
            

class Member(Profile):
    # attributes

But if a user is already having a relation with anyone, among both of them, then it should not be allowed to have a relation with the other one.

For example:
If a user1 is referenced by Leader model, then it is not allowed to be referenced by Member model, if needed there should be a process by which we can remove and add user from Leader model to Member model, i.e. transferring Profile abstract model data from Leader model to Member model and receiving remaining data manually or vica versa.

By searching over the internet, I got to know that to solve this there is a way of raising ValidationError, when saving the models as shown in above code, but in my case, the admin panel is used by a non-tech guy, by using above approach there will be a error screen showing my validation error, which will be unusual for them to understand easily.

What should be the better approach to implement this?
I am using VS Code 1.69.1, python 3.10.2 and django 4.0.3.
Thanks in Advance!

django-models django python
1 Answers

If you make the column "user" in Profile unique, then I believe the problem is solved.

class Profile(models.Model):
    user = models.OneToOneField(User, on_delete=models.DO_NOTHING, unique=True)

By the way, if the extended models "Leader" and "Member" could have the same questions/fields/columns then the best option was to delete both of them and just make in profile a column to distinguish the two because you can make also two seperate tables like this:

leaders = Profile.objects.filter(usertype=1) # 1=leader
members = Profile.objects.filter(usertype=2) # 2=member
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