The problem I'm running into is what to pass into contains_eager(). In
my table I'm mapping a file system, Asset.path is a unique constraint,
so my outerjoin() will either find a single row or none.
When I do:
--------------------
scn_alias=aliased(Asset)
p='testshow/eps/201/s22/t04'
take = session.query(Asset).filter(Asset.path==p).\
outerjoin((scn_alias,scn_alias.path=="%s/anim/scn"%p)).\
options(contains_eager(Asset,alias=scn_alias)).one()
-----------------------
I get:
Traceback (most recent call last):
File "<stdin>", line 3, in <module>
File "/usr/lib/pymodules/python2.5/sqlalchemy/orm/query.py", line 602,
in options
return self.__options(False, *args)
File "<string>", line 1, in <lambda>
File "/usr/lib/pymodules/python2.5/sqlalchemy/orm/query.py", line 52,
in generate
fn(self, *args[1:], **kw)
File "/usr/lib/pymodules/python2.5/sqlalchemy/orm/query.py", line 619,
in __options
opt.process_query(self)
File "/usr/lib/pymodules/python2.5/sqlalchemy/orm/interfaces.py", line
655, in process_query
self._process(query, True)
File "/usr/lib/pymodules/python2.5/sqlalchemy/orm/interfaces.py", line
661, in _process
paths = self.__get_paths(query, raiseerr)
File "/usr/lib/pymodules/python2.5/sqlalchemy/orm/interfaces.py", line
719, in __get_paths
raise sa_exc.ArgumentError("mapper option expects string key or list
of attributes")
sqlalchemy.exc.ArgumentError: mapper option expects string key or list
of attributes
Michael Bayer wrote:
> On May 1, 2009, at 2:55 PM, David Gardner wrote:
>
>
>> Along those same lines, one of the things I would like to do is to
>> do an arbitrary join, my table is hierarchical and often I want to
>> do a join against a a node, along with another node two levels deep
>> below it, and since its a tree structure eager loading all of the
>> children, and grandchildren would be costly, when I only care about
>> two of them.
>>
>> So I have this:
>>
>> scn_alias=aliased(Asset)
>> p='testshow/eps/201/s22/t04'
>>
>> take = session.query(Asset).filter(Asset.path==p).\
>> outerjoin((scn_alias,scn_alias.path=="%s/anim/
>> scn"%p),aliased=True).one()
>>
>> This produces the correct SQL, but since scn_alias isn't directly
>> mapped as a relation to the row I am querying, I can't figure out
>> the correct arguments to pass to contains_eager().
>>
>
> contains_eager just needs to know what columns in the selectable it
> needs to draw from. so again here, drop the aliased=True since
> scn_alias is already an alias, then pass scn_alias as the "alias"
> keyword to contains_eager(). Also your outerjoin should probably be
> qualified against the parent Asset object otherwise you're in danger
> of cartesian products.
>
>
>
> >
>
>
--
David Gardner
Pipeline Tools Programmer, "Sid the Science Kid"
Jim Henson Creature Shop
[email protected]
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