Is it possible to make child objects (many-to-one side) delete itself from
the old parent's collection when it is added to a different parent?
See the file attached. The old parent remains unaware that he doesn't have
this child anymore.
P.S. session.expire() is an obvious solution but too heavy. I expect some
event-based collection synchronization, much like backref (back_populates)
connected collections.
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
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from sqlalchemy import create_engine, MetaData, Column, String, ForeignKey
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy.ext.declarative import declarative_base
engine = create_engine('mysql://user@localhost/probe')
Base = declarative_base(bind=engine)
Session = sessionmaker(bind=engine)
session = Session()
class User(Base):
__tablename__ = 'user'
name = Column(String(10), primary_key=True)
address = relationship('Address', uselist=False, cascade='all,delete-orphan', back_populates='user')
class Address(Base):
__tablename__ = 'address'
addr = Column(String(20))
username = Column(ForeignKey(User.name), primary_key=True)
user = relationship('User', back_populates='address')
if __name__ == '__main__':
joe, jef = session.query(User).all()
if joe.name != 'joe':
joe, jef = jef, joe
assert joe.address is not None
assert jef.address is None
jef.address = joe.address
# HERE IS THE PROBLEM: it's expected to become None
assert joe.address is not None
session.flush()
assert joe.address is not None # not even flush() helps
# Here's how sample objects were created:
# Base.metadata.create_all()
# joe = User(name='joe')
# jef = User(name='jef')
# session.add_all((joe, jef))
# joe.address = Address(addr='joe str')
# session.commit()
