Hiya folks,
I'm having a problem defining a relationship between a model, and
another model that subclasses the first. ie:
class Page(models.Model):
...
sections = models.ManyToManyField('Section',
through='PageSection',
related_name='pages', symmetrical=False, blank=True,
null=True,)
class PageSection(models.Model):
"""An affiliation of a page with a section"""
page = models.ForeignKey('Page', related_name='page',)
section = models.ForeignKey('Page', related_name='section',)
weight = models.IntegerField(default=0,)
class Section(Page):
...
class Category(Section):
...
These models are defined in separate files, but have the
app_label='pages' option set in the Meta class (except for Category,
which is in a different app, but the relevant models of pages are
pulled in), so it syncdb's without issue.
I have a StackedInline ModelAdmin set up for PageSection, and it is in
the inlines list for Category's ModelAdmin.
Now, as I said, this syncdb's just fine, and the server runs, however
when I go to create a Category, I get:
<class 'pages.models.page.PageSection'> has more than 1 ForeignKey to
<class 'products.models.category.Category'>
Which I believe relates to this, from the docs:
"There are a few restrictions on the intermediate model:
Your intermediate model must contain one - and only one - foreign key
to the target model (this would be Person in our example). If you have
more than one foreign key, a validation error will be raised.
Your intermediate model must contain one - and only one - foreign key
to the source model (this would be Group in our example). If you have
more than one foreign key, a validation error will be raised.
The only exception to this is a model which has a many-to-many
relationship to itself, through an intermediary model. In this case,
two foreign keys to the same model are permitted, but they will be
treated as the two (different) sides of the many-to-many relation.
When defining a many-to-many relationship from a model to itself,
using an intermediary model, you must use symmetrical=False (see the
model field reference)."
The thing is, the intermediary model has FK's to different classes
(though one is a subclass of the other), and the error I'm getting
says that it is referencing the Category class twice, which it is -
it's referencing two different ancestors of it.
I know this seems unnecessarily complex, but this is how my project
has to be structured.
Does anyone have a work-around that will let me do what I want to?
Cheers.
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