Hi,
I do not understand the backref bit. With the setup as in the previous
reply the Applicant object can use anApplicant._state to get the State
object.
How can the State object get the related Applicant? Is a change in the
mapping needed? aState.applicant (as in backref) leads to
File "/usr/lib/pymodules/python2.5/sqlalchemy/orm/attributes.py",
line 588, in set
value = self.fire_replace_event(state, dict_, value, old,
initiator)
File "/usr/lib/pymodules/python2.5/sqlalchemy/orm/attributes.py",
line 608, in fire_replace_event
value = ext.set(state, value, previous, initiator or self)
File "/usr/lib/pymodules/python2.5/sqlalchemy/orm/attributes.py",
line 849, in set
initiator, passive=PASSIVE_NO_FETCH)
File "/usr/lib/pymodules/python2.5/sqlalchemy/orm/attributes.py",
line 394, in remove
self.set(state, dict_, None, initiator, passive=passive)
File "/usr/lib/pymodules/python2.5/sqlalchemy/orm/attributes.py",
line 584, in set
old = self.get(state, dict_)
RuntimeError: maximum recursion depth exceeded
Regards
Ernst
On Sep 11, 1:50 am, Ernst <[email protected]> wrote:
> Made two changes:
>
> applicant_table = Table('applicant', metadata,
> Column('id',Integer, primary_key=True), # not in model
> Column('state', Integer, ForeignKey('applicantstate.id')),
> )
>
> and
>
> mapper(Applicant.Applicant, applicant_table, properties={
> '_state':relation(Applicant.State, backref=backref('applicant',
> uselist=False))
>
> })
>
> and it does what I wished for. Being new I have to learn the basics:
> state is a foreign key in the database which the orm writes and _state
> is an attribute in the object which the orm 'assigns' on retrieval.
>
> Thank you
> Ernst
>
> On Sep 11, 12:39 am, Michael Bayer <[email protected]> wrote:
>
> > On Sep 10, 2010, at 3:14 AM, Ernst wrote:
>
> > > Hi,
> > > I have manged to set up joined and single table inheritance mappings.
> > > When relationships get involved I need help.
>
> > > I would like to use the state pattern. Class Applicant delegates to a
> > > subclass of State.
>
> > > applicant_table = Table('applicant', metadata,
> > > Column('applicant_id',Integer, primary_key=True),
> > > Column('_state', Integer, ForeignKey('applicantstate.state_id')),
> > > )
>
> > > appstate_table = Table('applicantstate', metadata,
> > > Column('state_id',Integer, primary_key=True),
> > > Column('type', String(30),nullable=False),
> > > Column('_givenName', String(40))
> > > )
>
> > > # applicant - state relationship, one to one, SQLAlchemy-0.5.8-
> > > #mapper(Applicant, applicant_table, properties={
> > > # 'applicantstate':relation(State, uselist=False,
> > > backref='applicant')
> > > #})
>
> > > mapper(Applicant, applicant_table, properties={
> > > 'applicantstate':relation(State, backref=backref('applicant',
> > > uselist=False))
> > > })
>
> > > I tried both relationships and get:
> > > ProgrammingError: (ProgrammingError) can't adapt '
> > > INSERT INTO applicant (applicant_id, _state)
> > > VALUES (%(applicant_id)s, %(_state)s)'
> > > {'_state': <tg21tut.model.Applicant2.NewStdApp object at 0x9034bec>,
> > > 'applicant_id': 1L}
>
> > > I have omitted the single table inheritance mappings.
>
> > The relationship is valid. The error there arises from some inappropriate
> > manipulation of objects, such as setting applicant._state =
> > SomeApplicantState(), instead of assigning to the "applicantstate"
> > attribute. Full detail would be needed in order to determine the issue.
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