[Sqlalchemy-tickets] [sqlalchemy] #2743: Backref broken for detached objects

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

#2743: Backref broken for detached objects
----------------------+-----------------------------------------
 Reporter:  schlamar  |           Owner:  zzzeek
     Type:  defect    |          Status:  new
 Priority:  medium    |       Milestone:
Component:  orm       |        Severity:  no triage selected yet
 Keywords:            |  Progress State:  awaiting triage
----------------------+-----------------------------------------
 You cannot traverse a backref if the object is detached and the
 relationship is already joined.

 Testcase:


 {{{
 #!python
 Base = declarative_base()


 class Parent(Base):
     __tablename__ = 'parent'
     id = Column(Integer, primary_key=True)


 class Child(Base):
     __tablename__ = 'child'
     id = Column(Integer, primary_key=True)
     parent_id = Column(Integer, ForeignKey('parent.id'))
     parent = relationship('Parent', backref='children')


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

     p = Parent()
     p.children.append(Child())
     session.add(p)
     session.commit()

     parents = session.query(Parent).options(joinedload('children')).all()
     session.expunge_all()
     print parents
     print parents[0].children
     print parents[0].children[0].parent
 }}}

 Fails with:

 {{{
 Traceback (most recent call last):
   File "testcase.py", line 44, in <module>
     main()
   File "testcase.py", line 35, in main
     print parents[0].children[0].parent
   File
 "/Users/marc/Documents/python/sqlalchemy/lib/sqlalchemy/orm/attributes.py",
 line 316, in __get__
     return self.impl.get(instance_state(instance), dict_)
   File
 "/Users/marc/Documents/python/sqlalchemy/lib/sqlalchemy/orm/attributes.py",
 line 613, in get
     value = self.callable_(state, passive)
   File
 "/Users/marc/Documents/python/sqlalchemy/lib/sqlalchemy/orm/strategies.py",
 line 497, in _load_for_state
     (orm_util.state_str(state), self.key)
 sqlalchemy.orm.exc.DetachedInstanceError: Parent instance <Child at
 0x10654ffd0> is not bound to a Session; lazy load operation of attribute
 'parent' cannot proceed

 }}}

--
Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2743>
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