For instance :
|
>>>fromdbaccess import*# import engine, models, etc.
>>>Dispositif.hardware_collection.attr # doesn't exist yet
Traceback(most recent call last):
File"<stdin>",line 1,in<module>
File"/usr/local/lib/python2.7/dist-packages/sqlalchemy/ext/associationproxy.py",line
204,inattr
return(self.local_attr,self.remote_attr)
File"/usr/local/lib/python2.7/dist-packages/sqlalchemy/ext/associationproxy.py",line
184,inlocal_attr
returngetattr(self.owning_class,self.target_collection)
AttributeError:type object'Dispositif'has noattribute
'disp_hdw_collection'
>>>dir(Dispositif)# there is no 'disp_hdw_collection', but
'hardware_collection' exists (seems because I define it explicitely)
[...,'classes','hardware_collection','id','metadata','prepare']
>>>session =Session()# create the first session
>>>l =session.query(Dispositif).all()# first query call, takes about 2s
>>>Dispositif.hardware_collection.attr # now exists...
(<sqlalchemy.orm.attributes.InstrumentedAttributeobjectat
0x148edb0>,<sqlalchemy.orm.attributes.InstrumentedAttributeobjectat
0x12f2f90>)
>>>dir(Dispositif)# many news relationships and collections appear here
[...,'classes','disp_hdw_collection','hardware_collection','id','metadata','prepare',<some_more_collections...>]
|
Le lundi 31 août 2015 16:33:52 UTC+3, Michael Bayer a écrit :
On 8/31/15 8:23 AM, yoch....@gmail.com <javascript:> 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 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')
class
|
...
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