Mike Conley wrote:
> What is correct way to join two subqueries? The example is somewhat
> contrived, but illustrates the problem.
>
> SQL might look like this
>
> SELECT x.blah, y.blah
> FROM (SELECT id, data AS blah FROM a) AS x
> JOIN (SELECT id, data AS blah FROM b) AS y
> ON x.id = y.id
>
> Mapped classes are:
>
> class A(Base):
> __tablename__ = 'a'
> id = Column(Integer, primary_key=True)
> data = Column(String)
> def __repr__(s):
> return '<A id:%s data:%s>' % (s.id, s.data)
>
> class B(Base):
> __tablename__ = 'b'
> id = Column(Integer, primary_key=True)
> data = Column(String)
> def __repr__(s):
> return '<B id:%s data:%s>' % (s.id, s.data)
>
> with some data:
>
> session.add_all([A(data='a1'),A(data='a2'),B(data='b1'),B(data='b2'),])
> session.commit()
>
> and subqueries:
>
> subqa = session.query(A.id, A.data.label('blah')).subquery()
> subqb = session.query(B.id, B.data.label('blah')).subquery()
>
> First attempt:
>
> session.query(subqa.c.blah, subqb.c.blah)
>
> as expected this give a cross join of all A's and B's
>
> Second attempt:
>
> session.query(subqa.c.blah,
> subqb.c.blah).join((subqb,subqb.c.id==subqa.c.id
> ))
>
> gives and error:
> AttributeError: 'NoneType' object has no attribute 'base_mapper'
>
> probably because subqa is not a mapped entity
uhhh yeah. its trying to find the source to join from. you don't
actually need the "join()" here you could just filter on
subqb.c.id==subqa.c.id. If you really want JOIN or OUTERJOIN, do
q.select_from(subqa.join(subqb, ...)).
as far as q.join() figuring that out, that might be a little tough to
implement though we can maybe make the error message do a better job. ill
add a ticket.
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