[FIXED] Django model class inheritance - default fields and overrides

Issue

I'm attempting to have inherited class templates, so that all my models have certain default fields, and all have default overrides for a few functions like save_model()

If I do it like this, I get the overrides, but then have to go and manually set meta data like db_table...

class ModelExtension(models.Model):
    altered_by = models.CharField(max_length=64)

class SomeModel(ModelExtension):
    class Meta:
        db_table = 'app_somemodel'
    fields = models.CharField()
    ...

Is there a way to get this kind of inheritance working right? So far I either have to do extra work to compensate for the drawbacks of this approach, or I'm plagued by MRO errors.2

Solution

What's an MRO error? Have you read the django docs on model inheritance? You can either have Abstract Base Classes, Multi-table inheritance, or proxy models.

http://docs.djangoproject.com/en/stable/topics/db/models/#abstract-base-classes

What you've done there is a multi-table inheritance - there's a hidden OneToOneField connecting your two models. I don't know why you think you need the db_table specified - it shouldn't be.

If you are never going to have objects of bare class ModelExtension then you want abstract base classes. In this case you put abstract=True in the Meta section, and then all the fields from the base class are added to the table for the child class. The docs explain it better than I can here.

I often find myself starting to do it one way and then flipping back and forth several times as I think more about my database structure....

Answered By - Spacedman