Re: Bug in model inheritance?

As to whether it's a bug or not I have no idea, though it seems so.

If you use:

entity = models.OneToOneField(Entity, parent_link=True, primary_key=True)

it will create the primary key in both Kid and Adult tables, which
sounds like what you want?

On Tue, Sep 28, 2010 at 1:06 PM, phill <famousactress@gmail.com> wrote:
> This looks quite a bit like a bug, but we may be off the reservation
> in terms of how we're using the product. (Disclaimer: I'm relatively
> new to Django, and extremely new to the codebase that I ran into this
> on).
>
> We've got a form of schema-inheritance going on in this project in
> order to accomplish shared-id-space and the ability to relate models
> to one of a number of different types. The way that we've broken it
> out runs us into a strange inconsistency in Django that specifically
> affects our ability to serialize the objects. Here's a simplified
> version of what we're doing:
>
> class Entity(models.Model):
>    entityType = models.CharField(editable=False,max_length=50)
>
>    def __init__(self, *args, **kwargs):
>        super(Entity, self).__init__(*args, **kwargs)
>        self.entityType = self.__class__.__name__
>
>    def __unicode__(self):
>        return 'Entity: %s %s' %(self.entityType, self.id)
>
> class BasePerson(Entity):
>
>    entity = models.OneToOneField(Entity, parent_link=True)
>    name = models.CharField(max_length=50)
>
>    class Meta:
>        abstract = True
>
> class Kid(BasePerson):
>    school = models.CharField(max_length=50)
>
> class Adult(BasePerson):
>    job = models.CharField(max_length=50)
>
>
>
> When I dump instances of these models out using the standard fixtures
> serialization, instances of Kid will serialize the 'entity' field, but
> instances of Adult won't. The reason is because Adult's entity field
> is marked primaryKey=True. Kid's is not. There appears to be a caching
> issue here, because if I swap the order that Kid and Adult are defined
> in.. the error reverses (now Kid's field will be marked pk).
>
> Is this a bug? If not, what's the reasoning behind this behavior? Is
> there a better pattern for accomplishing this kind of inheritance?
>
> Thanks in advance for your help.
>
> Phill
>
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