Michael Bayer wrote:
> also your example should read like this:
>
> a = session.query(A).all()[0]
> print a.time_units
> a.time_units = 1
> print a.time_units
> #print A.timeunits
> #print A.time_units
>
Huh ? time_units is the column name in the database. I want to refer to
that column through the attribute 'timeunits'. I also want to use
descriptors to do extra work when setting that attribute. The synonym
api docs say:
*def synonym(/name/, /map_column=False/, /descriptor=None/, /proxy=False/)*
Set up name as a synonym to another mapped property.
So when I say:
mapper(A, table_A, properties = {
"time_units" : synonym("timeunits", map_column = True)
})
Am I not saying 'create an alias to column 'time_units' in table_A and
call it 'timeunits' ??
Incidentally.. creating this mapping replaces the existing property/data
descriptor class variable with an instance of a Mapper:
print A.timeunits
mapper(A, table_A, properties = {
"time_units" : synonym("timeunits", map_column = True)
})
print A.timeunits
>> ./test.py
<property object at 0x848c3ec>
<Mapper at 0x84e5d4c; A>.timeunits
Unless Mapper takes special care of any existing descriptors how can
they co-exist with mapped attributes ?
--
t o b e
> the A.time_units is the class-bound descriptor so that raises an
> exception due to a missing __str__() method. this is a small bug but
> does not break the functionality you're looking for. The in-python
> access to the attribute is performed via the attribute you've created,
> i.e. a.time_units.
>
>
> On Jan 26, 2009, at 12:59 PM, Toby Bradshaw wrote:
>
>> CREATE TABLE example_a
>> (
>> id integer NOT NULL,
>> time_units integer,
>> CONSTRAINT example_a_pkey PRIMARY KEY (id)
>> )
>>
>> and (based on
>> http://www.sqlalchemy.org/docs/05/mappers.html#using-descriptors)
>> <http://www.sqlalchemy.org/docs/05/mappers.html#using-descriptors%29>:
>>
>> from sqlalchemy import *
>> from sqlalchemy.orm import sessionmaker, mapper, synonym
>>
>> class A(object):
>> def _set_t(self, t):
>> print "SET"
>> self.timeunits = t / float(10)
>> def _get_t(self):
>> print "GET"
>> return self.timeunits * 10
>> time_units = property(_get_t, _set_t)
>>
>> engine = create_engine("postgres://tobe:<snip>@localhost/test")
>> engine.echo = False
>>
>> session_class = sessionmaker(
>> bind = engine, autoflush = True, autocommit = False,
>> )
>>
>> meta = MetaData(bind = engine)
>> table_A = Table("example_a", meta, autoload = True)
>>
>> print A.time_units
>> mapper(A, table_A, properties = {
>> "time_units" : synonym("timeunits", map_column = True)
>> })
>>
>> session = session_class()
>>
>> a = session.query(A).all()[0]
>> print a.timeunits
>> a.timeunits = 1
>> print a.timeunits
>> print A.timeunits
>> print A.time_units
>
>
> >
--
t o b e
--
A truly clever developer will create code so easy to understand that a less
than average developer could debug it.
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