[Django]-Multiple models with similar fields Django

You can make an abstract base class [Django-doc] that implements the common logic, and then inherit:

class MyBaseClass(models.Model):
    id = models.CharField(max_length=8, primary_key=True)
    first_name = models.CharField(max_length=128)
    last_name = models.CharField(max_length=128)
    pin_code = models.CharField(max_length=128)

    def save(self, *args, **kwargs):
        model = self._meta.model
        if not self.pk:
            id = secrets.token_urlsafe(8)
            while model.objects.filter(id=id).exists():
                id = secrets.token_urlsafe(8)
            self.id = id
        super().save(*args, **kwargs)

    class Meta:
        abstract = True

class User(MyBaseClass):
    pass

class Customer(MyBaseClass):
    pass

An abstract class will thus not construct a table, it basically is used to inherit fields, methods, etc. to avoid rewriting the same logic twice.