Django: How to Auto-Populate field with a related-model's field

Question

I have two basic models:

class ModelA(models.model):
    ... #some fields
    score = models.IntegerField()

class ModelB(models.model)
    ... #some fields
    related_model=models.OneToOneField(ModelA)
    score = models.IntegerField(default=related_model.score)

What I want is that upon creation of ModelB, it's score field be filled with the value of score of ModelA to which it has a OneToOne relation.

I have tried setting the score = models.IntegerField(default=related_model.score) but upon migration I get the error: AttributeError: 'OneToOneField' object has no attribute 'score'

I also tried defining a method under ModelB as follows and passing it to the default:

def get_score(self, *args, **kwargs):
    return self.threat.score

This doesn't work either. when I set default=get_score() I get the error: missing one required positional argument: self

How can I automatically set a model's field to be a field of it's related model's (by OneToOne Relation) field?

Answer 1

You should do this on save.

def save(self, *args, **kwargs):
    if not self.score:
        self.score = self.threat.score
    return super().save(*args, **kwargs)