[sqlalchemy] order_by on a relationship() ?

[Julien Cigar]

Hello all,

always with the following:
orm.mapper(Human, table.human)

orm.mapper(Content, table.content,
  polymorphic_on = table.content.c.content_type_id,
  properties = {
    'owner' : orm.relationship(
                Human,
                lazy = 'joined',
                innerjoin = True,
            )
  }
)

Is there a way to order_by on the 'owner' property of the Content mapper 
directly without having to join the related class (Human in this case) 
again ?

I thought something like :

Content.query.filter(Content.container_id==789).\
  order_by(Content.owner.login)

but it doesn't work : AttributeError: Neither 'InstrumentedAttribute' 
object nor 'Comparator' object has an attribute 'login'

It works with
Content.query.join(Human).\
  filter(Content.container_id==789).\
  order_by(Human.login)

but then Human is joined two times, one for the explicit .join() and one 
for the 'owner' relationship (... JOIN human ON human.id = 
content.owner_id JOIN human AS human_1 ON human_1.id = content.owner_id ...)

Also, if I put lazy = 'select' in place of lazy = 'joined' for the above 
relationship() and that I do :

Content.query.join(Human).\
  filter(Content.container_id==789).\
  order_by(Human.login)

and then if I access the 'owner' property of one of those selected 
objects SQLAlchemy issues a SELECT again, .. why ? Is there a way to 
tell SQLAlchemy that the .join(Human) of the above query is in fact the 
'owner' property of Content .. ?

Thanks,
Julien

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