On 8/31/15 8:23 AM, yoch.me...@gmail.com wrote:
Thank you very much.
Le lundi 31 août 2015 06:17:37 UTC+3, Michael Bayer a écrit :
On 8/29/15 2:27 PM, yoch....@gmail.com <javascript:> 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 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.
OK.
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
<http://docs.sqlalchemy.org/en/rel_1_0/orm/loading_relationships.html>
If I try :
|
>>>x
=db.query(Dispositif).options(joinedload(Dispositif.hardware_collection)).get(2721)
|
I got an error : sqlalchemy.exc.ArgumentError: mapper option expects
string key or list of attributes.
if 'hardware_collection' is the association proxy, right now you can't
pass it directly like that; you can use the helper "attr" with
joinedload_all:
query.options(joinedload_all(*Dispostif.hardware_collection.attr))
or use the actual relationships:
quey.options(joinedload(Dispotif.attribute_a).joinedload(DispToHardware.attribute_b))
But it's still possible to "preload" the association part by using :
|
>>>x
=db.query(Dispositif).options(joinedload(Dispositif.disp_hdw_collection)).get(2721)
|
So calling x.hardware_collection after that produce only one query.
Is there a better way to do ?
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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