I didn't think it would be, but it is a bug, yes, am applying the patch in
http://www.sqlalchemy.org/trac/ticket/2759 right now.
On Jun 14, 2013, at 11:52 PM, Seth P <spadow...@gmail.com> wrote:
> I've encountered what I believe to be a bug in SQLAlchemy (versions 0.8.0 and
> 0.8.1) in a query that joins class/tables that use joined inheritance.
>
> In the code below, I would expect the three queries to produce the same
> output, namely [u'CCC'], but the first one gives a different (incorrect)
> result, [u'BBB']. Is this a bug, or is the query malformed?
> In the second query, adding a seemingly gratuitous join with D fixes the
> problem. And as the third query shows, replacing C by an aliased version also
> fixes the problem. So whatever is going on seems rather subtle.
>
> Thanks,
>
> Seth
>
>
>
> from sqlalchemy import Column, Integer, String, ForeignKey, create_engine
> from sqlalchemy.ext.declarative.api import declarative_base
> from sqlalchemy.orm import relationship, sessionmaker, scoped_session
> from sqlalchemy.orm.util import aliased
>
> Base = declarative_base(object)
> metadata = Base.metadata
>
> class A(Base):
> __tablename__ = 'A'
> idx = Column(Integer, primary_key=True)
> name = Column(String(20), nullable=False)
> type_idx = Column(Integer, nullable=False)
> __mapper_args__ = { 'polymorphic_on':type_idx }
>
> class B(A):
> __tablename__ = 'B'
> idx = Column(Integer, ForeignKey(str(A.__table__) + ".idx"),
> primary_key=True)
> __mapper_args__ = { 'polymorphic_identity':2 }
>
> class C(A):
> __tablename__ = 'C'
> idx = Column(Integer, ForeignKey(str(A.__table__) + ".idx"),
> primary_key=True)
> b_idx = Column(Integer, ForeignKey(str(B.__table__) + ".idx"),
> nullable=False)
> b = relationship("B", foreign_keys=[b_idx])
> __mapper_args__ = { 'polymorphic_identity':3 }
>
> class D(A):
> __tablename__ = 'D'
> idx = Column(Integer, ForeignKey(str(A.__table__) + ".idx"),
> primary_key=True)
> __mapper_args__ = { 'polymorphic_identity':4 }
>
> class CtoD(Base):
> __tablename__ = 'CtoD'
> idx = Column(Integer, primary_key=True)
> c_idx = Column(Integer, ForeignKey(str(C.__table__) + ".idx"),
> nullable=False)
> c = relationship("C", foreign_keys=[c_idx])
> d_idx = Column(Integer, ForeignKey(str(D.__table__) + ".idx"),
> nullable=False)
> d = relationship("D", foreign_keys=[d_idx])
>
> if __name__ == '__main__':
> engine = create_engine('sqlite:///:memory:', echo=False)
> metadata.create_all(bind=engine)
> Session = scoped_session(sessionmaker(bind=engine))
> session = Session()
>
> # populate tables with a single entry in each table
> b = B(name='BBB')
> c = C(name='CCC', b=b)
> d = D(name='DDD')
> c_to_d = CtoD(c=c, d=d)
> session.add_all([b, c, d, c_to_d])
> session.commit()
>
> sql_query = session.query(B, C.name).join(C, B.idx == C.b_idx).join(CtoD,
> C.idx == CtoD.c_idx).join(D, CtoD.d_idx == D.idx)
> print [name for (_, name) in sql_query.all()] # [u'BBB']
>
> sql_query = session.query(B, C.name).join(C, B.idx == C.b_idx).join(CtoD,
> C.idx == CtoD.c_idx)
> print [name for (_, name) in sql_query.all()] # [u'CCC']
>
> aliased_C = aliased(C)
> sql_query = session.query(B, aliased_C.name).join(aliased_C, B.idx ==
> aliased_C.b_idx).join(CtoD, aliased_C.idx == CtoD.c_idx).join(D, CtoD.d_idx
> == D.idx).join(D, CtoD.d_idx == D.idx)
> print [name for (_, name) in sql_query.all()] # [u'CCC']
>
>
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