Hi,
Could anyone help point me in the right direction here? Any help would
be much appreciated!
Thanks,
Jesse
On May 30, 12:54 pm, Jesse Cohen <ske...@gmail.com> wrote:
> This is my first post here, I've been learning about the query api and I've
> got three related questions:
>
> 1. Suppose I have a User model and UserThing which is loaded into the
> User.things collection, UserThing is polymorphic via joined table
> inheritance. I'd like to do something like this:
>
> subq = s.query(UserThing).with_polymorphic('*').with_labels().subquery()
> users_with_eagerly_loaded_things = s.query(User).join(subq,
> User.things).options(contains_eager(User.things, alias=subq)).all()
>
> This works, the query appears to be rendered correctly, and the base-class
> attributes of the collection are populated eagerly and work fine, but the
> polymorphic attributes (attributes unique to the inherited classes) of the
> collections aren't populated, so when I do:
>
> print users_with_eagerly_loaded_things[0].some_polylmorphic_attribute
>
> Sqlalchemy issues more sql to fetch those attributes even though they were
> already fetched in the subquery and should have been populated by the
> contains_eager option. It is as if the subquery only queried the table for
> the base class, even though I have verified that when I add the
> with_polymorphic('*') it joins against all the inherited tables as well.
> What am I doing wrong? In addition to doing this via a query, is there an
> attribute I can specify on a collection to have that collection always use a
> polymorphic eager load?
>
> 2. On a similar note, suppose if in that join I want to specify a join
> condition manually, how do I refer to the alias of the subquery -- I cant
> seem to figure out the syntax of that, e.g.
>
> s.query(User).join(subq, subq.user_id == User.id) #(but subq.user_id
> gives me an error)
>
> 3. One final question, suppose I want an explicit join kind of like this
> that returns tuples of (User, UserThing):
>
> s.query(User, UserThing).join(subq).all()
>
> but the above will give me a cartesian product of Users and UserThings,
> because sqlalchemy doesn't know that the subquery is specifying UserThings.
> What I really want is results returned as the subq joined to the user in a
> tuple, this works
>
> s.query(User, subq).join(subq)
>
> but doesn't return results in the form I want. I get all of the fields of
> the subquery individually rather than nicely being populated into a
> UserThing object, e.g. results look like (User, userthing_id,
> userthing_name, userthing_data). How do I get this query to return results
> that look like (User,UserThing) if the UserThings are fetched via a
> subquery?
>
> Finally, I also just wanted to say how awesome I find your software -- I
> just started using sqlalchemy about a month ago and every time I need to do
> something I am amazed by how sqlalchemy handles it and how much easier it
> makes my life as well as the extensive support community which exists.
>
> Thanks!!
>
> Best,
> Jesse Cohen
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