@update:
calling the flush doen't seem to make any difference. At some point, the
object looses track of it's grandparents
On Tuesday, August 22, 2017 at 3:57:23 PM UTC+2, cecemel wrote:
>
> Hi,
>
> so, I'm currently facing this issue, where I would like to do some calls
> to an external service, when my object has been deleted within a flush.
> For this operation to occur, I need the id from my model object, but also
> the id from the parent of the parent object model. There are cases, where I
> am unable to access them (I guess, depending of the order of the execution)
> and I am unsure on what to do next.
>
> So if you're willing to give me some advice, would be awesome.
>
> Here is a dummy model:
>
> from sqlalchemy import event
>
> from sqlalchemy import *
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.orm import sessionmaker, backref, relationship
>
> Base = declarative_base()
>
>
> #########################################################################################
> # MODEL
> #########################################################################################
> class House(Base):
> __tablename__ = 'house'
> id = Column(Integer, primary_key=True)
> rooms = relationship("Room",
> backref=backref("house", lazy="joined"),
> cascade='all, delete-orphan')
>
>
> class Room(Base):
> __tablename__ = 'room'
> id = Column(Integer, primary_key=True)
> house_id = Column(Integer, ForeignKey('house.id'))
> beds = relationship("Bed",
> backref=backref("room", lazy="joined"),
> cascade='all, delete-orphan')
>
>
> class Bed(Base):
> __tablename__ = 'bed'
> id = Column(Integer, primary_key=True)
> room_id = Column(Integer, ForeignKey('room.id'))
>
>
> #########################################################################################
> # CONFIG
> #########################################################################################
> def setup():
> engine = create_engine("sqlite:///foo.db", echo=True)
>
> Base.metadata.bind = engine
> Base.metadata.create_all(engine)
>
> SessionFactory = sessionmaker(
> bind=engine
> )
>
> event.listen(SessionFactory, 'deleted_to_detached',
> listener_bed_has_been_removed)
>
> return SessionFactory
>
>
> def listener_bed_has_been_removed(session, instance):
> if type(instance) is not Bed:
> return
>
> bed_id = instance.id
> house_id = instance.room.house.id # this is NOT ALWAYS there. Depending
> on the order of the execution I guess
>
> print("execute the service call to external service here bed_id {},
> house_id {}".format(bed_id, house_id))
>
>
>
>
> So my question(s):
>
> - Is there a clean way to always acces this parent's parent attribute?
> - If not, would be starting a new session and query it from the
> event handler be an option? (is it not dangerous, because it seems to
> work)
> - Additional quirk, I am working within a transaction manager
> (pyramid_tm) and ZopeTransactionExtension()
>
> Thanks!
>
>
> More information about the system:
>
> SQLAlchemy 1.1.13
>
> Python 3.5
>
> Postgres 9.6
>
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The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
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