you can either make a non-primary mapper() for the class with “include_attributes” and set that as the target of the relationship, or you can use the new load_only() loader option at query time.
On Nov 18, 2013, at 3:27 PM, Jonathan Vanasco <[email protected]> wrote: > this is just wild thinking -- and might not be possible. > > > I'm wondering if anyone has some ideas on creating a relationship where only > certain columns are queried during relationship loading. > > I have a few relationships like this ( pseudocode ) > > class Tag2Posting: > tag_id INT > posting_id INT > > tag = sa.relationship( Tag ) > posting = sa.relationship( Posting ) > > > class Tag: > id > name > to_postings = sa.relationship( Tag2Posting ) > > > class Posting: > id INT > to_tags = sa.relationship( Tag2Posting ) > > > accessing the relationship will pull the entire object. > > posting_a.to_tags -->generates--> "SELECT tag_id , posting_id FROM > tag_2_posting" > > > I really only care about the "tag_id" , so I'd want to create a relationship > that generates this sql : > > "SELECT tag_id FROM tag_2_posting" > > that would probably create either an array of ids: > > posting_a.tag_ids = [1,2,3] > > > a similar , but different, concept would be an object where certain columns > are Deferred when loaded through a relationship ( and normal otherwise ). > > > this is a bad example, because i'm using a 2 column association object. but > it makes a lot of sense when there's no association object and you end up > querying a ton of data that will not be used. > > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/sqlalchemy. > For more options, visit https://groups.google.com/groups/opt_out.
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