[Sqlalchemy-tickets] [sqlalchemy] #2762: Relationship lazy configuration doesn't work with polymorphism

[sqlalchemy <mi...@zz...>]

#2762: Relationship lazy configuration doesn't work with polymorphism
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 Reporter:  schlamar  |           Owner:  zzzeek
     Type:  defect    |          Status:  new
 Priority:  medium    |       Milestone:
Component:  orm       |        Severity:  no triage selected yet
 Keywords:            |  Progress State:  awaiting triage
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 Testcase:


 {{{
 #!python

 from sqlalchemy import create_engine, Column, ForeignKey, Integer
 from sqlalchemy.orm import relationship, sessionmaker
 from sqlalchemy.ext.declarative import declarative_base

 Base = declarative_base()


 class RelatedModel(Base):
     __tablename__ = 'related_model'
     id = Column(Integer, primary_key=True)


 class Model(Base):
     __tablename__ = 'model'
     id = Column(Integer, primary_key=True)

     mtype = Column(Integer, nullable=False)
     __mapper_args__ = {'polymorphic_on': mtype}


 class SubModel(Model):
     __tablename__ = 'submodel'
     id = Column(Integer, ForeignKey('model.id'), primary_key=True)
     __mapper_args__ = {'polymorphic_identity': 1}

     related_model_id = Column(Integer, ForeignKey('related_model.id'))
     related_model = relationship('RelatedModel', lazy='joined')


 def main():
     engine = create_engine('sqlite:///:memory:')
     Base.metadata.create_all(engine)
     Session = sessionmaker(bind=engine)
     session = Session()

     s = SubModel()
     s.related_model = RelatedModel()
     session.add(s)

     session.commit()
     session.close()

     session = Session()
     s = session.query(Model).one()
     session.close()
     s.related_model
 }}}

 I expect that the relationship `SubModel -> RelatedModel` is already
 loaded, even when querying against the base class. However, the above code
 raises `DetachedInstanceError: Parent instance <SubModel at 0x2b465f0> is
 not bound to a Session; lazy load operation of attribute 'related_model'
 cannot proceed`.

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Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2762>
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