For Django recursive ManytoManyFields, can related_name override symmetrical=False?

Question

I have a few recursive Django ManytoManyField's that use the 'through attribute' in my app. here is an example:

class Author(models.Model):
    user = models.OneToOneField(User, parent_link=True)
    introduction = models.TextField(blank=True)
    pictures = models.ManyToManyField('Graphic', related_name='users', null=True)
    organizations = models.ManyToManyField('Organization', related_name='members')
    expertise = models.ManyToManyField('Tag', related_name='experts', null=True)
    interests = models.ManyToManyField('Tag', related_name='interested_in', null=True)
    saved_articles = models.ManyToManyField(Article, related_name='favorited_by', null=True, through='SavedArticles')
    authors_followed = models.ManyToManyField('self', related_name='authors_followed', null=True, through='FollowedAuthors', symmetrical=False)

class FollowedAuthors(models.Model):
    author = models.ForeignKey(Author)
    trustee = models.ForeignKey(Author)
    notes = models.TextField()
    tags = models.ManyToManyField('Tag')

I know I could access MyAuthor.authors_followed.all(), but if I wanted call FollowedAuthor.authors_followed.all() to return MyAuthor, couldn't I just use related_name='authors_followed'? Does that just negate the symmetrical=False behavior?

A similar question was asked here, but in that case they had:

recursive_field = models.ManyToManyField('self', through='ThroughTable', related_name='different_field').

Am I missing some understanding of how symmetrical and related_name work?

score 2 · Accepted Answer · answered Mar 15 '12 at 16:31

2

If I understand correctly, I think you should have something like:

authors_followed = models.ManytoManyField('self', related_name='following_authors', null=True, through='FollowedAuthors', symmetrical=False)

That way,

MyAuthor.following_authors.all()

will return the authors that are following MyAuthor, and

MyAuthor.author_followed.all()

will return the authors that MyAuthor is following.

With your configuration, Django is not able to make the difference and identify the direction you want.

answered Mar 15 '12 at 16:31

Arthur

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Thanks, yeah I understand that. But I want MyAuthor.authors_followed.all() to return both authors that MyAuthor follows and authors that follow MyAuthor indistinguishably - as a sort of mutual friendship. Is Django going to raise an error when I try to syncdb with the code I have? – Eric H. Mar 15 '12 at 18:00
oh, ok, I didn't get that. You could try "python manage.py validate" if you don't want to syncdb. I think it won't work the way you have it. (Actually, I _hope_ it won't work). Two options then: 1. you could drop the symmetrical=False, but I guess you put it here for a reason; 2. create a function, maybe a property, that would gather the whole family (following and followed authors). – Arthur Mar 15 '12 at 18:11
Ahhh ha. Yes I was kinda hoping it wouldn't work either and it didn't when I ran manage.py validate. Error states: Reverse query name 'authors_followed' clashes with m2m field Author.authors_followed. I'll have to write the function merging the querysets like you suggested. – Eric H. Mar 15 '12 at 18:47
Looks like django doesn't let you have your asymmetrical and not eat it too (consume it with 2 queries). Sorry for the triple-negative brain twister. – hobs Jun 16 '12 at 01:25

For Django recursive ManytoManyFields, can related_name override symmetrical=False?

1 Answers1