Django Models: Common Ancestor Inheritance & Migration

Question

I thought I would up my python game with Django a bit by developing a large scale business app for fun. I seen the need for a common ancestor approach to model inheritence and tried to implement it based on the official documentation. However, I keep getting this very annoying Message which I'm not sure what to do with.

Dj Version: Django 1.7
Py Version: Python 3.4.2

Message

$ python manage.py makemigrations

You are trying to add a non-nullable field 'businessentity_ptr' to business without a default; we can't do that (the database needs something to populate existing rows).

Please select a fix:
 1) Provide a one-off default now (will be set on all existing rows)
 2) Quit, and let me add a default in models.py

Models.py

class BusinessEntity(models.Model):
    title = models.CharField(max_length=180)

    def __str__(self):
        return self.title


class Business(BusinessEntity):
    description = models.TextField(max_length=600)
    claimed = models.BooleanField(default=False)
    slug = models.SlugField()
    timestamp = models.DateTimeField(auto_now_add=True, auto_now=False)
    updated = models.DateTimeField(auto_now_add=False, auto_now=True)

    def __str__(self):
        return self.description

What I've Tried, (which everyone will hate):

Deleting the DB & Re-migrating
setting a default value for all fields
Setting all fields to null = True

I have seen a hack around for this but I don't think it's a good approach. Maybe there is someone out there who understand Django Common Ancestors much better and point me in the right direction.

Do you need BusinessEntity to be an actual concrete model that you can query? Otherwise it would be better as an abstract model, and your problem wouldn't happen. — Daniel Roseman, Nov 06 '14 at 13:04
Django inheritance for models can get messy (even with mixins instead of concrete ancestors). I regret having used it in my current project. I found a lot of corner cases the [POLA](http://en.wikipedia.org/wiki/Principle_of_least_astonishment) is violated. — Paulo Scardine, Nov 06 '14 at 13:05
@DanielRoseman yeah, it's just abstract. There is no need to query over the BusinessEntity object. — ham-sandwich, Nov 06 '14 at 13:10

score 10 · Accepted Answer · answered Nov 06 '14 at 13:15

Since your parent model is intended to be abstract, you should mark it as such.

class BusinessEntity(models.Model):
    title = models.CharField(max_length=180)

    class Meta:
        abstract = True

This prevents Django from creating a separate table for it, and therefore needing a _ptr field to point back to it from the subclass. Instead, the table for your subclass will be created to include the inherited field(s) directly.

Django Models: Common Ancestor Inheritance & Migration

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