On 8/29/15 2:27 PM, yoch.me...@gmail.com wrote:
Thanks for the reply.
Le vendredi 28 août 2015 18:52:37 UTC+3, Michael Bayer a écrit :
On 8/28/15 3:51 AM, yoch....@gmail.com <javascript:> wrote:
Another question is why sqlalchemy produce two queries to get
hardwares collections from a dispositif :
|
>>>some_disp.hardwares
2015-08-2810:36:41,722INFO sqlalchemy.engine.base.EngineSELECT
disp_hdw.iddispositif AS
disp_hdw_iddispositif,disp_hdw.idhardware AS
disp_hdw_idhardware,disp_hdw.instance AS disp_hdw_instance
FROM disp_hdw
WHERE %s =disp_hdw.iddispositif
2015-08-2810:36:41,725INFO sqlalchemy.engine.base.Engine(2721L,)
2015-08-2810:36:41,768INFO sqlalchemy.engine.base.EngineSELECT
hardware.hdw_type AS hardware_hdw_type,hardware.id AS
hardware_id,hardware.idbox AS hardware_idbox
FROM hardware
WHERE hardware.id =%s
2015-08-2810:36:41,772INFO sqlalchemy.engine.base.Engine(268L,)
|
There's no context given here, but that would indicate that the
"some_disp" instance has been expired. When you .commit() a
session, all objects are expired by default. This is so that if,
when you next operate on the objects, some other transaction has
deleted that row, the session can let you know that you're working
on stale data. See the session docs for options on how to
control this behavior.
Here the context, all in the same session :
|
>>>fromdbaccess import*# import engine, Base and tables objects
>>>fromsqlalchemy.orm.session importsessionmaker
>>>Session=sessionmaker(bind=engine)
>>>session =Session()
>>>l =session.query(Dispositif).all()
>>>some_disp =l[-2]
>>>engine.echo =True
>>>some_disp.hardwares
2015-08-2920:34:30,972INFO sqlalchemy.engine.base.EngineSELECT
disp_hdw.iddispositif AS disp_hdw_iddispositif,disp_hdw.idhardware AS
disp_hdw_idhardware,disp_hdw.instance AS disp_hdw_instance
FROM disp_hdw
WHERE %s =disp_hdw.iddispositif
2015-08-2920:34:30,975INFO sqlalchemy.engine.base.Engine(2721L,)
2015-08-2920:34:31,018INFO sqlalchemy.engine.base.EngineSELECT
hardware.hdw_type AS hardware_hdw_type,hardware.id AS
hardware_id,hardware.idbox AS hardware_idbox
FROM hardware
WHERE hardware.id =%s
2015-08-2920:34:31,022INFO sqlalchemy.engine.base.Engine(268L,)
|
oh. Well this is association proxy, which means it needs to load two
separate relationships, so that is two SELECT statements with default
loader strategy.
In fact, /hardwares/ can be retrieved in one query.
instead of somewhat like :
|
SELECT hardware.hdw_type AS hardware_hdw_type,hardware.id AS
hardware_id,hardware.idbox AS hardware_idbox
FROM hardware
JOIN disp_hdw ON hardware.id =disp_hdw.idhardware
WHERE disp_hdw.iddispositif =%s
|
sure thing, use joined eager loading:
http://docs.sqlalchemy.org/en/rel_1_0/orm/loading_relationships.html
||
Le vendredi 28 août 2015 10:20:55 UTC+3, yoch....@gmail.com a
écrit :
Hello,
I want to use assocation proxy pattern
<http://docs.sqlalchemy.org/en/latest/orm/extensions/associationproxy.html>
with automap. I tried this code :
|
Base=automap_base()
classDispositif(Base):
__tablename__ ='dispositifs'
hardwares =association_proxy('disp_hardwares','hardware')
classHardware(Base):
__tablename__ ='hardware'
Base.prepare(engine,reflect=True)
|
but it does not work.
Any help appreciated.
Best regards
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