Hello,
For 1-to-1 model relationships, when relationship value is updated, the
default SQLAlchemy behavior is to set the foreign key column of previous
relationship value to NULL.
I would like to configure SQLAlchemy to not set the foreign key column to
NULL, but instead to set a `deleted` flag to true. This will allow me to
have historical data.
Having read docs on cascade, I have not found an option that can configure
this. Is this doable?
Here is a test I want passing
from sqlalchemy import Column, Integer, String, ForeignKey, Boolean
from sqlalchemy import create_engine, and_
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
from sqlalchemy.orm import sessionmaker
Base = declarative_base()
engine = create_engine('sqlite:///:memory:', echo=True)
Session = sessionmaker(bind=engine)
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
_address = relationship("Address",
primaryjoin=lambda: and_(Address.user_id ==
User.id,
~Address.deleted),
uselist=False,
back_populates="user")
@property
def address(self):
return self._address
@address.setter
def address(self, new_address):
if self._address:
self._address.deleted = True
self._address = new_address
class Address(Base):
__tablename__ = 'addresses'
id = Column(Integer, primary_key=True)
email = Column(String, nullable=False)
deleted = Column(Boolean, nullable=False, default=False)
user_id = Column(Integer, ForeignKey('users.id'))
user = relationship("User")
def test():
Base.metadata.create_all(engine)
sess = Session()
a1 = Address(email='foo')
u = User(id=1, address=a1)
sess.add_all([u, a1])
sess.commit()
u.address = Address(email='bar')
sess.commit()
assert a1.user_id == 1, a1.user_id
test()
Thanks in advance
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