Jared Nuzzolillo wrote:
> Greetings!
>
> I've known about sqlalchemy for a long time and have been interested in
> using it professionally for a while now. I finally have the chance to use
> it
> and have really been enjoying it. But it turns out that I am a little
> confused about the best way to handle m2m relationships that have
> additional
> fields.
>
> Let's say we have 4 tables, User, Tag, Post, PostTagAssociation.
> PostTagAssociation has FKs of course, but also a tagged_at datetime field.
>
> I am familiar with association_proxy, but I prefer a different sort of
> interface. Something closer to dynamic_loader that would let me do things
> like:
>
> #querying across my dynamic_loader:
> post = test_user.posts.filter(Post.
> title.like('%geopolitic%')).first()
> #query through an association proxy, eg to get all posts tagged with war
> related keywords:
> #of course, this doesn't work since it returns an AssociationList instead
> of
> an AppenderQuery:
> post.tags.filter(Tag.name.like('%war%'))
> #and then i still want to be able to have the AssociationList
> functionality
> like:
> post.tags.append(Tag("peace"))
> post.tags.remove(Tag("war"))
> #what would be really amazing is if I could set it up to decorate
> #the returned item with some or all fields from the m2m table, eg:
> print post.tags.first().tagged_at # => 10/27/2009 21:24
>
> This seems like it would be commonly desired functionality, so I am
> wondering if perhaps: a) I missed it, and there is some option already in
> sqlalchemy, or b) Someone already has created an extension that provides
> this.
>
> If not, I wonder if supplying a new query class to the query_class option
> of
> dynamic_loader might be able to accomplish this.I'm assuming Post.tags is an associationproxy. So dynamic_loader isn't used here (that only applies to a relation()), you'd be looking to build an associationproxy that produces a Query() when called upon. So you really want to build an associationproxy._AssociationCollection subclass that does what you'd like, and specify it using proxy_factory and proxy_bulk_set on the associationproxy. Because the proxied collection lives outside of what the unit of work cares about, it doesn't need all the weird stuff that dynamic_loader has to do in order to work with the ORM, so should be fairly straightforward to create. Does that strategy make > sense? Are there any examples around that supply a query_class to the > dynamic_loader function? I couldn't find any, though I definitely might > have > missed them. > > I know it's also possible that am thinking about this all wrong, asking > the > wrong question since I am used to other kinds of ORMs. If so, I'd love to > hear how experienced sqlalchemy users achieve this same sort of > functionality (eg, do they manually add methods to their model classes > that > work directly with the association table and do a subquery, or something > completely different?) > > Thank you so very much, and please excuse the long post. > > Best! > Jared Nuzzolillo > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
