Thank you very much Simon! I skipped those parts without realizing how
useful they are. Thanks a lot for point me the right direction!
On Wed, Jun 18, 2014 at 3:57 AM, Simon King <si...@simonking.org.uk> wrote:
> On Wed, Jun 18, 2014 at 8:40 AM, Bao Niu <niuba...@gmail.com> wrote:
> > I have a Person class and a Names class, which have a one-to-many
> > relationship ( a person can have many names ).
> >
> > After doing a query like this:
> >>
> >> p = session.query(Person).filter(Person.birthday > "1992-01-01").one()
> >
> >
> > I'd like to further perform a query on the returned object p to select
> only
> > its names that starts with letter "B".
> >
> > Currently I am using a very basic way of looping(by the way I'm using
> > automap bases, which is cool!) :
> >>
> >> for n in p.names_collection:
> >> if n.startswith('B'):
> >> names.append(n)
> >
> >
> > I'm wondering if there is some sqlalchemy-specific ways of querying an
> > attributes on a returned object? Just need a hint here, I can do the
> > research following the lead. Many thanks.
> >
>
> There's a couple of ways of doing this, and which you use really
> depends on your use case.
>
> One option is to explicitly query the Names table, using the
> "with_parent" method to restrict the results to names belonging to the
> correct person:
>
> name_query =
> session.query(Names).with_parent(p).filter(Names.name.startswith('B'))
>
>
> http://docs.sqlalchemy.org/en/rel_0_9/orm/tutorial.html#common-relationship-operators
>
> Another is to configure the relationship as "dynamic":
>
>
> http://docs.sqlalchemy.org/en/rel_0_9/orm/collections.html#dynamic-relationship
>
> If you do this, Person.names_collection will no longer be a simple
> Python list, but instead a special kind of query that is preconfigured
> to select rows related to the person instance. You would use it like:
>
> name_query = p.names_collection.filter(Names.name.startswith('B'))
>
> This usually only makes sense for very large collections, since you
> can't really eager-load a dynamic relationship.
>
> Hope that helps,
>
> Simon
>
> --
> You received this message because you are subscribed to a topic in the
> Google Groups "sqlalchemy" group.
> To unsubscribe from this topic, visit
> https://groups.google.com/d/topic/sqlalchemy/AyLtTlVfwvs/unsubscribe.
> To unsubscribe from this group and all its topics, send an email to
> sqlalchemy+unsubscr...@googlegroups.com.
> To post to this group, send email to sqlalchemy@googlegroups.com.
> Visit this group at http://groups.google.com/group/sqlalchemy.
> For more options, visit https://groups.google.com/d/optout.
>
--
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 sqlalchemy+unsubscr...@googlegroups.com.
To post to this group, send email to sqlalchemy@googlegroups.com.
Visit this group at http://groups.google.com/group/sqlalchemy.
For more options, visit https://groups.google.com/d/optout.
