Thank you, that helps!
-Eric
On Sunday, July 24, 2016 at 7:57:18 PM UTC-4, Eric Wittle wrote:
>
> I'd like to understand the behavior of association_proxy when creating new
> records across a many-to-many table where, in some cases, the joining table
> will have additional attribute values beyond the two primary keys. In the
> below example, there is a many-many between Person and Events represented
> by the PersonEvents table. If I create and commit the person record, create
> and commit the event record, and then add the event to the person and try
> to commit, I get a key error. If I create the Person record, create the
> Event record, and then create the PersonEvent record before committing, I
> get no error and my tests pass.
>
> There are two differences in the test approaches that I think I
> understand; in the failing case the PersonEvent object is being created
> implicitly through the association proxy definition, and the commit order
> is different. However, as I read the documentation, I don't understand why
> the results are different. I'd like to avoid building more complex logic
> until I understand whether the association_proxy has use case limitations I
> don't understand.
>
> Here's the data model code:
>
> class Person(Base):
> __tablename__ = 'Person'
> __table_args__ = {'mysql_charset':'utf8'}
> id = Column(Integer, primary_key=True)
> full_name = Column(String(240))
>
> email = Column(String(120),unique=True)
> other_data = Column(JSON)
> events = association_proxy('PersonEvent','Event')
>
>
> class PersonEvent(Base):
> __tablename__ = 'PersonEvent';
> __tableargs__ = {'mysql_charset':'utf8'}
> person_id = Column(Integer, ForeignKey('Person.id'), primary_key=True)
> event_id = Column(Integer, ForeignKey('Event.id'), primary_key = True)
> role = Column(String(40))
>
>
> # bi-directional attribute / collection of "Person" / "Event"
> person = relationship('Person',
> backref=backref("PersonEvent",
> cascade="all, delete-orphan"))
>
> # reference to the Event object
> event = relationship('Event')
>
>
> class Event(Base):
> __tablename__ = 'Event'
> __table_args__ = {'mysql_charset':'utf8'}
> id = Column(Integer, primary_key=True)
> start = Column(DateTime)
> end = Column(DateTime)
> short_name = Column(String(40))
> name = Column(String(240))
> other_data = Column(JSON)
>
> The following code in the test setup method throws a KeyError on the last
> commit from emit_backref_from_scalar_set_event child_impl =
> child_state.manager[key].impl.
>
> session = DBSession()
> p1 = Person(id=1, first_name='Eric', last_name='Wittle',
> full_name='Eric L. Wittle', email='z...@wittle.net
> <e...@wittle.net>')
> p1.set('favorite_color','red')
> session.add(p1)
> session.commit()
> logger.debug('Added person 1')
> e1 = Event(id=1, name='Birth',
> start=datetime.strptime('01/25/1976',"%m/%d/%Y"),
> end=datetime.strptime('01/25/1976',"%m/%d/%Y"))
> session.add(e1)
> session.commit()
> logger.debug('Added event 1')
> p1.events.append(e1)
> session.add(p1)
> session.commit()
>
> However, if I replace it with the code below, the data setup completes
> without error, and the test passes fine (looking up person with id 1 and
> testing if the property events[0].name == 'Birth'):
>
> session = DBSession()
> p1 = Person(id=1, first_name='Eric', last_name='Wittle',
> full_name='Eric L. Wittle', email='z...@wittle.net
> <e...@wittle.net>')
> p1.set('favorite_color','red')
> e1 = Event(id=1, name='Birth',
> start=datetime.strptime('01/25/1976',"%m/%d/%Y"),
> end=datetime.strptime('01/25/1976',"%m/%d/%Y"))
> pe1 = PersonEvent(person=p1, event=e1, role = 'Owner')
> session.add(p1)
> session.commit()
>
> The first set of code that fails seems more similar to the example in the
> association proxy documentation, section "Simplifying Association Objects"
> than the code that passes.
>
> Thanks in advance for any advice & guidance. I've been really impressed
> with the sqlalchemy orm so far, and am trying to use more of it.
>
> -Eric
>
>
>
>
>
>
>
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