sqlalchemy relationships are currently only "fully" loading - meaning
you cant directly filter on an instances collection attribute.
however you can construct your own query based on the relationship
and use that, and theres plenty of tools to make that easy.
such as, if you set up a bi-directional relationship:
class A(object):pass
class B(object):pass
mapper(B, b_table)
mapper(A, a_table, properties={
"b_collection" : relation(A, secondary=a_to_b_table,
backref="a_collection")
})
if you load an instance of "A":
mya = session.query(A).select(a.id=7)
you can query the "B"s on an "A" via the backref:
result = session.query(B).filter_by(a_collection=mya).filter
(A.c.somecriterion=='foo').list()
theres also some patterns for dealing with large collections at:
http://www.sqlalchemy.org/docs/
adv_datamapping.html#advdatamapping_properties_working
On Apr 2, 2007, at 7:44 AM, Kaali wrote:
>
> Can i use ORM many-to-many relations and filter SQL -side? If i can't,
> can you give me an example on how i should use many-to-many relations
> with filtering in SQLAlchemy?
>
> --
> K
>
> On Apr 2, 1:36 pm, svilen <[EMAIL PROTECTED]> wrote:
>>> After getting the results, i will filter them with Python filters,
>>> as i don't know how to filter many-to-many queries directly.
>>
>>> Should i somehow make custom queries that handles many-to-many
>>> relationships etc. or is there something else i'm missing that
>>> makes the system slow? I have ran the bench with MySQL and
>>> PostgreSQL engines, the result is the same. When running with a
>>> profiler, at least ~90% of the time is taken by SQLAlchemy.
>>
>> one general suggestion, try to move the filtering on the sql side;
>> thus u'll have less data transferred then instantiated then
>> filtered - which is probably eating most of the time.
>
>
> >
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