Re: [sqlalchemy] Re: getting model's grandparent after persistent_to_deleted event has fired.

[Felix Ruiz de Arcaute]

ok thanks. Unfortunately, I'll have to mess with my data model, but if
there is no other way, I'll do it like that.

On Wed, Aug 23, 2017 at 4:19 AM, Mike Bayer 
wrote:

> On Tue, Aug 22, 2017 at 6:46 PM, cecemel  wrote:
> > Hello,
> >
> > thanks again for the answer. Perhaps my case was not clear enough. To
> make
> > it a bit more explicit, I updated the example accordingly.
> >
> > 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://", 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
> >
> > # so, in this example, this function should be called 3 times.
> > # The first time it is called, I get no problems, I can access
> > instance.room.house_id the call proceeds
> > # The second bed is a problem, I get the error
> > # "sqlalchemy.orm.exc.DetachedInstanceError: Parent instance  > 0x7f24fe14bb70> is not bound to a Session; lazy load operation of
> attribute
> > 'room' cannot proceed"
> >
> > # SO, my question is: is there ANY way to keep these references to
> > parents in this function?
> >
> > bed_id = instance.id
> > house_id = instance.room.house_id
> >
> >
> > print("execute a service call to external service here bed_id {},
> > house_id {}".format(bed_id, house_id))
> >
> >
> > if __name__ == "__main__":
> > session_factory = setup()
> > session = session_factory()
> >
> > session.add(House(id=1))
> > session.add(Room(id=1, house_id=1))
> > session.add(Bed(id=1, room_id=1))
> > session.add(Bed(id=2, room_id=1))
> > session.add(Bed(id=3, room_id=1))
> > session.commit()
> >
> > room = session.query(Room).get(1)
> > session.delete(room)
> > session.commit()
> > session.close()
> >
> >
> > So, for this example, I am looking for a solution to keep the references
> to
> > the 'house' from the 'bed' model after flush (any solution would be
> good).
> > Is there perhaps a way to dynamically set a property in 'bed' -model (e.g
> > house_id), once 'room'-backref has been loaded ?
>
> so the way you have this set up, you have not only room->bed but you
> also have delete,delete-orphan cascade.  this indicates your intent
> that a Bed object should be deleted when it is both not associated
> with any Room, as well as when its parent Room is deleted.   So the
> behavior you are getting is what you specified.
>
> if you *dont* want Bed to be deleted when Room is deleted, you'd want
> to remove that delete-orphan casacde.  If you then want Bed to be
> directly associated with House in the absense of Room, then yes you'd
> add another column house_id to Bed with a corresponding
> relationship(), and you'd need to make sure that is assigned as you
> want as well when the objects go into the database.
>
>
>
>
>
> >
> >
> > On Tuesday, August 22, 2017 at 5:36:39 PM UTC+2, Mike Bayer wrote:
> >>
> >> you would need to illustrate an MCVE of what's happening.  objects
> >> don't "lose track" of their related objects unless yes, you deleted
> >> them, in which case you should not expect that they would be there.
> >> when the object is expired, it will go to reload them, and they'll be
> >> gone.
> >>
> >> On Tue, Aug 22, 2017 at 

Re: [sqlalchemy] Re: getting model's grandparent after persistent_to_deleted event has fired.

[Mike Bayer]

On Tue, Aug 22, 2017 at 6:46 PM, cecemel  wrote:
> Hello,
>
> thanks again for the answer. Perhaps my case was not clear enough. To make
> it a bit more explicit, I updated the example accordingly.
>
> 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://", 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
>
> # so, in this example, this function should be called 3 times.
> # The first time it is called, I get no problems, I can access
> instance.room.house_id the call proceeds
> # The second bed is a problem, I get the error
> # "sqlalchemy.orm.exc.DetachedInstanceError: Parent instance  0x7f24fe14bb70> is not bound to a Session; lazy load operation of attribute
> 'room' cannot proceed"
>
> # SO, my question is: is there ANY way to keep these references to
> parents in this function?
>
> bed_id = instance.id
> house_id = instance.room.house_id
>
>
> print("execute a service call to external service here bed_id {},
> house_id {}".format(bed_id, house_id))
>
>
> if __name__ == "__main__":
> session_factory = setup()
> session = session_factory()
>
> session.add(House(id=1))
> session.add(Room(id=1, house_id=1))
> session.add(Bed(id=1, room_id=1))
> session.add(Bed(id=2, room_id=1))
> session.add(Bed(id=3, room_id=1))
> session.commit()
>
> room = session.query(Room).get(1)
> session.delete(room)
> session.commit()
> session.close()
>
>
> So, for this example, I am looking for a solution to keep the references to
> the 'house' from the 'bed' model after flush (any solution would be good).
> Is there perhaps a way to dynamically set a property in 'bed' -model (e.g
> house_id), once 'room'-backref has been loaded ?

so the way you have this set up, you have not only room->bed but you
also have delete,delete-orphan cascade.  this indicates your intent
that a Bed object should be deleted when it is both not associated
with any Room, as well as when its parent Room is deleted.   So the
behavior you are getting is what you specified.

if you *dont* want Bed to be deleted when Room is deleted, you'd want
to remove that delete-orphan casacde.  If you then want Bed to be
directly associated with House in the absense of Room, then yes you'd
add another column house_id to Bed with a corresponding
relationship(), and you'd need to make sure that is assigned as you
want as well when the objects go into the database.





>
>
> On Tuesday, August 22, 2017 at 5:36:39 PM UTC+2, Mike Bayer wrote:
>>
>> you would need to illustrate an MCVE of what's happening.  objects
>> don't "lose track" of their related objects unless yes, you deleted
>> them, in which case you should not expect that they would be there.
>> when the object is expired, it will go to reload them, and they'll be
>> gone.
>>
>> On Tue, Aug 22, 2017 at 11:05 AM, cecemel  wrote:
>> > @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 

Re: [sqlalchemy] Re: getting model's grandparent after persistent_to_deleted event has fired.

[cecemel]

Hello, 

thanks again for the answer. Perhaps my case was not clear enough. To make 
it a bit more explicit, I updated the example accordingly. 

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://", 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

# so, in this example, this function should be called 3 times.
# The first time it is called, I get no problems, I can access 
instance.room.house_id the call proceeds
# The second bed is a problem, I get the error
# "sqlalchemy.orm.exc.DetachedInstanceError: Parent instance  is not bound to a Session; lazy load operation of attribute 
'room' cannot proceed"

# SO, my question is: is there ANY way to keep these references to parents 
in this function?

bed_id = instance.id
house_id = instance.room.house_id


print("execute a service call to external service here bed_id {}, house_id 
{}".format(bed_id, house_id))


if __name__ == "__main__":
session_factory = setup()
session = session_factory()

session.add(House(id=1))
session.add(Room(id=1, house_id=1))
session.add(Bed(id=1, room_id=1))
session.add(Bed(id=2, room_id=1))
session.add(Bed(id=3, room_id=1))
session.commit()

room = session.query(Room).get(1)
session.delete(room)
session.commit()
session.close()


So, for this example, I am looking for a solution to keep the references to 
the 'house' from the 'bed' model after flush (any solution would be good). 
Is there perhaps a way to dynamically set a property in 'bed' -model (e.g 
house_id), once 'room'-backref has been loaded ?


On Tuesday, August 22, 2017 at 5:36:39 PM UTC+2, Mike Bayer wrote:
>
> you would need to illustrate an MCVE of what's happening.  objects 
> don't "lose track" of their related objects unless yes, you deleted 
> them, in which case you should not expect that they would be there. 
> when the object is expired, it will go to reload them, and they'll be 
> gone. 
>
> On Tue, Aug 22, 2017 at 11:05 AM, cecemel  > wrote: 
> > @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, 

Re: [sqlalchemy] Re: getting model's grandparent after persistent_to_deleted event has fired.

[Mike Bayer]

you would need to illustrate an MCVE of what's happening.  objects
don't "lose track" of their related objects unless yes, you deleted
them, in which case you should not expect that they would be there.
when the object is expired, it will go to reload them, and they'll be
gone.

On Tue, Aug 22, 2017 at 11:05 AM, cecemel  wrote:
> @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
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
> description.
> ---
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-- 
SQLAlchemy - 
The Python SQL Toolkit and Object Relational Mapper

http://www.sqlalchemy.org/

To post example code, please provide an MCVE: Minimal, Complete, and Verifiable 
Example.  See  http://stackoverflow.com/help/mcve for a full description.
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[sqlalchemy] Re: getting model's grandparent after persistent_to_deleted event has fired.

[cecemel]

@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
>

-- 
SQLAlchemy - 
The Python SQL Toolkit and Object Relational Mapper

http://www.sqlalchemy.org/

To post example code, please provide an MCVE: Minimal, Complete, and Verifiable 
Example.  See  http://stackoverflow.com/help/mcve for a full description.
--- 
You received this message because you are subscribed to the Google Groups 
"sqlalchemy" group.
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