On Wed, Feb 7, 2018 at 7:16 AM, tonthon <tontho...@gmail.com> wrote:
> Hi,
>
> I'd like to setup bidirectionnal data synchornization between the lastname
> attribute of two related models
>
> class User(Base):
> __tablename__ = 'users'
> id = Column(Integer, primary_key=True)
> lastname = Column(String(50))
> userdatas = relationship('UserDatas',
> primaryjoin='User.id==UserDatas.user_id', back_populates='user',
> uselist=False)
>
> class UserDatas(Base):
> __tablename__ = 'userdatas'
> id = Column(Integer, primary_key=True)
> lastname = Column(String(50))
> user_id = Column(ForeignKey('users.id'))
> user = relationship('User', primaryjoin='User.id==UserDatas.user_id')
>
>
> I thought I could do something like this :
>
> def sync_lastname_user_to_userdatas(target, value, oldvalue, initiator):
> target.userdatas.lastname = value
>
> listen(User.lastname, 'set', sync_lastname_user_to_userdatas)
>
> def sync_lastname_userdatas_to_user(target, value, oldvalue, initiator):
> target.user.lastname = value
>
> listen(UserDatas.lastname, 'set', sync_lastname_userdatas_to_user)
>
>
> The obvious problem here is the infinite loop that is generated
>
> So :
> Is there a way to set an attribute without firing the 'set' event ?
>
> I tend to think there is a better way to do that, does anybody have an
> advice to share ?
below is an example of the most correct way to do this, to support
this use case I will add the "initiator" argument to the
set_attribute() function within SQLAlchemy but this will work in all
1.1, 1.2 versions for now:
from sqlalchemy import Column, Integer, String, ForeignKey
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import event
from sqlalchemy import inspect
def set_attribute(instance, key, value, initiator=None):
"""Set the value of an attribute, firing history events.
This function is copied from the attributes module but adds the
"initiator" argument.
"""
state = inspect(instance)
dict_ = state.dict
state.manager[key].impl.set(state, dict_, value, initiator)
Base = declarative_base()
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
lastname = Column(String(50))
userdatas = relationship(
'UserDatas', primaryjoin='User.id==UserDatas.user_id',
back_populates='user', uselist=False)
class UserDatas(Base):
__tablename__ = 'userdatas'
id = Column(Integer, primary_key=True)
lastname = Column(String(50))
user_id = Column(ForeignKey('users.id'))
user = relationship('User', primaryjoin='User.id==UserDatas.user_id')
@event.listens_for(User.lastname, "set")
def sync_lastname_user_to_userdatas(target, value, oldvalue, initiator):
parentclass = initiator.parent_token.parent.class_
if parentclass is User:
set_attribute(target.userdatas, "lastname", value, initiator)
@event.listens_for(UserDatas.lastname, 'set')
def sync_lastname_userdatas_to_user(target, value, oldvalue, initiator):
parentclass = initiator.parent_token.parent.class_
if parentclass is UserDatas:
set_attribute(target.user, "lastname", value, initiator)
u1 = User(userdatas=UserDatas())
u1.lastname = 'foo'
assert u1.userdatas.lastname == u1.lastname == 'foo'
u1.userdatas.lastname = 'bar'
assert u1.userdatas.lastname == u1.lastname == 'bar'
>
> Thanks in advance
>
> Regards,
> Gaston Tjebbes
>
> https://www.majerti.fr
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
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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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