Interesting, and I had thought about it, but wouldn't that run the subquery (myselect) 3 times for each join?
On Sunday, April 20, 2014 10:01:20 PM UTC-4, Michael Bayer wrote: > > there’s a way to get the tuple comparison to work here though it’s not as > common, I’d have to try it out and there might be some quirks to work out. > I would think this would be more straightforward using a straight AND: > > and_(mo.c.col1 == myselect.c.col1, mo.c.col2 == myselect.c.col2, mo.c.col3 > == myselect.c.col3) > > where “myselect” is like: select([…]).where(…).alias() > > > On Apr 20, 2014, at 9:33 PM, Rick Otten <rottenw...@gmail.com<javascript:>> > wrote: > > So FWIW, for now, I cast all three columns into strings and concatenated > them using the column_property() expression in the mapper, and then did the > comparison on that. It worked ok to create the join condition I needed. > It wasn't a pretty as a tuple comparison but it got the job done and I can > hit my deadline for tomorrow morning. > > > On Sunday, April 20, 2014 2:38:21 PM UTC-4, Rick Otten wrote: >> >> I would like to apply a condition in an outer join that matches a >> multi-item list rather than a single value. >> >> In other words, I'm trying to get SQLAlchemy 0.8.6 connecting to >> PostgreSQL 9.3.4 to generate SQL like this: >> >> >> >> select >>> * >>> from >>> mytable mt >>> left outer join myothertable mo on >>> (m0.col1, m0.col2, mo.col3) = (select m2.col1, m2.col2, >>> m2.col3 >>> from >>> myothertable m2 >>> where mt.col1 = >>> m2.wilson_id >>> order by >>> m2.col3 desc >>> limit 1) >> >> >> >> When I construct my query object back in Python 2.7: >> mo = aliased(myothertable) >> m2 = aliased(myothertable) >> mySession.query(mytable, myothertable)\ >> .select_from(mytable)\ >> .outerjoin(mo, >> [mo.col1, mo.col2, mo.col3] == select(\ >> [m2.col1, m2.col2, m2.col3])\ >> .where(m2.col1 == mytable.col1)\ >> .order_by(m2.col3.desc())\ >> .limit(1)) >> >> >> I get: >> >> File "build/bdist.linux-x86_64/egg/sqlalchemy/orm/query.py", line 1699, >> in outerjoin >> File "<string>", line 1, in <lambda> >> File "build/bdist.linux-x86_64/egg/sqlalchemy/orm/query.py", line 51, >> in generate >> File "build/bdist.linux-x86_64/egg/sqlalchemy/orm/query.py", line 1816, >> in _join >> File "build/bdist.linux-x86_64/egg/sqlalchemy/orm/query.py", line 1846, >> in _join_left_to_right >> File "build/bdist.linux-x86_64/egg/sqlalchemy/orm/query.py", line 1861, >> in _prepare_right_side >> File "build/bdist.linux-x86_64/egg/sqlalchemy/inspection.py", line 74, >> in inspect >> *sqlalchemy.exc.NoInspectionAvailable: No inspection system is available >> for object of type <type 'bool'>* >> >> >> I tried both List type and Tuple type in my comparison from the inner >> select statement. >> When I look at the code where this exception is thrown, it suggests that >> something is wrong with my mapping. >> >> I've done this join by comparing a single column with these two tables, >> and I've done similar things with other single column comparisons. I'm not >> sure why I'm unable to compare a set of columns instead. >> >> I've been pondering casting all three columns to string and then >> concatenating them (either in the table mapping, or in the query) to see if >> I can get back to a single value comparision which I expect to work. I'd >> rather just compare the tuple/lists though. >> >> I could use some hints. If you guys have some. Thanks! >> >> >> >> >> > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sqlalchemy+...@googlegroups.com <javascript:>. > To post to this group, send email to sqlal...@googlegroups.com<javascript:> > . > Visit this group at http://groups.google.com/group/sqlalchemy. > For more options, visit https://groups.google.com/d/optout. > > > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
