Awesome ultra-speedy reply!. I thought I might have to tell the mapper
about how to join. I will try that approach.
The "query(Country).filter(Country.id==CountrySynonym.country_id)"
doesn't work for me because I want to do an outer join.
Thanks for the documentation link. I shall begin reading. :)
Kind Regards
Crispin Wellington
On Mar 27, 3:58 am, Michael Bayer <[EMAIL PROTECTED]> wrote:
> On Mar 26, 11:46 pm, Crispin Wellington <[EMAIL PROTECTED]>
> wrote:
>
>
>
>
>
> > select * from countries left join country_synonyms;
>
> > Here are my attempts and their results:
>
> > >>> Session.query(Country).join(CountrySynonym).all()
> > InvalidRequestError: Mapper 'Mapper|Country|countries' has no property
> > '<class 'helloworld.model.CountrySynonym'>'
>
> > >>> Session.query(Country,CountrySynonym).join(CountrySynonym).all()
>
> > InvalidRequestError: Mapper 'Mapper|Country|countries' has no property
> > '<class 'helloworld.model.CountrySynonym'>'
>
> > >>> Session.query(Country).join(CountrySynonym.country_id).all()
>
> > AttributeError: 'ColumnProperty' object has no attribute
> > '_is_self_referential'
>
> > And so on...
>
> query.join() only joins on relations that you set up between mappers.
> so if you set up your mappers like:
>
> mapper(Country, countries, properties={
> 'synonyms':relation(CountrySynonym)
>
> })
>
> mapper(CountrySynonym, country_synonyms)
>
> then your join would just be:
>
> query(Country).join('synonyms')
>
> if you want to join tables together where you haven't told your
> mappers about their relationship (or you want to join in some other
> way besides whats configured), then you use the Table objects again,
> but you can still use them with Query via select_from()
>
> query(Country).select_from(countries.join(country_synonyms))...
>
> With a regular inner join like you're doing, theres also just setting
> it up in the WHERE criterion:
>
> query(Country).filter(Country.id==CountrySynonym.country_id)....
>
> > All the docs use a Table() based approach like
> > "sql.execute(countries.join(country_synonyms)..." but I want to use
> > the Mapped objects as that's what I'm using everywhere else. I've
> > found the docs on sqlalchemy to focus on the Table() and engine based
> > interfaces, but the docs focusing on objects and sessions leave a lot
> > of guessing.
>
> Plenty of docs on the subject in the ORM tutorial. For examples of
> query.join(), see:
>
> http://www.sqlalchemy.org/docs/04/ormtutorial.html#datamapping_joins
>
> other important ORM chapters are "Mapper Configuration" and "Using the
> Session".
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