OneToOne and ForeignKey related objects are cached differently

[Maniac <Maniac@…>]

Looks like ForeignKeys respect model's custom default manager and OneToOneField don't. Here's an example.

There are 3 models: Author, Article and Contact. Article refers to Author with ForeignKey and Contact refers to Author with OneToOneField. Author has a custom default manager that gives out only authors with their 'available' field set to True:

class AvailableAuthorManager(models.Manager):
  def get_query_set(self):
    return super(AvailableAuthorManager, self).get_query_set().filter(available__exact=True)

class Author(models.Model):
  name = models.CharField(maxlength=50)
  available = models.BooleanField(default=True)
  
  objects = AvailableAuthorManager()
  
class Article(models.Model):
  author = models.ForeignKey(Author)
  title = models.CharField(maxlength=50)
  
class Contact(models.Model):
  author = models.OneToOneField(Author)
  address = models.CharField(maxlength=50)

Then if you have an author with available=False and an article and a contact reefering to it you get:

• article.author -- raises an exception DoesNotExist
• contact.author -- returns the author

Looks like this should behave the same way in both cases. However I'm not sure how exactly but I tend to think that it should raise an exception because managers are supposed to be the ultimate mechanism to access model objects.

[James Bennett]

Using the models and manager outlined here, I created one Author, and an Article and a Contact related to it. Then I set the Author's 'available' field to False and got a DoesNotExist exception for both 'article.author' and 'contact.author'. Maybe we're on different revisions and something changed between them?

[Maniac <Maniac@…>]

I tested it further and it seems you're right. The behavior that I was observing was caused by caching objects:

author = Author(name='...')
author.save()
article = Article(author=author, title='...')
article.save()
contact = Contact(author=author, address='...')
contact.save()

article.author  # OK
contact.author  # OK

author.available=False
author.save()

article.author  # Exception
contact.author  # OK

So it seems that accessing object through OneToOne does use cached object and ForeignKey does a query. I'm changing summary appropriately. Now I think cached version should be used in both cases because caches are usually expected to be out of sync with reality.

[Maniac <Maniac@…>]

Here's more. If you get a contact or an article with select_related() you will always have their authors. I mean selected_related() seems to not use managers at all.

I sorts understand why is this happening but I'm not very familiar with this code. May be I should file another bug for this?

[Ivan Sagalaev]

This is actually long fixed. ForeignKey's and OneToOne behave now consistently (though they do omit default manager on purpose).