Thank, I haven't yet figured out how to make your code more general
(without having to specify 'user_id'), but I think it can be done.
In the meantime I came up with a somewhat gross solution of my own.
The idea is to declare relation as `viewonly=True` and to delegate sets
to an injected write-only relationship (injection is the gross part).
I'm curious to hear your opinion on this approach, if possible.
Here is the code:
>
> from sqlalchemy import Column, Integer, String, ForeignKey, Boolean
> from sqlalchemy import create_engine, and_
> from sqlalchemy import event
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.orm import relationship, mapper
> from sqlalchemy.orm import sessionmaker
>
>
> Base = declarative_base()
> engine = create_engine('sqlite:///:memory:', echo=False)
> Session = sessionmaker(bind=engine)
>
>
> def soft_deleting_relationship(target, primaryjoin):
> assert issubclass(target, Base)
> rel = relationship(target,
> primaryjoin=primaryjoin,
> viewonly=True,
> uselist=False,
> )
>
> @event.listens_for(mapper, 'after_configured', once=True)
> def configure():
>
> key = '_all_child_' + rel.key
> parent = rel.parent.class_
> if not hasattr(parent, key):
> setattr(parent, key, relationship(target, lazy="noload"))
>
> @event.listens_for(rel, 'set', active_history=True)
> def set(target, value, oldvalue, initiator):
> if oldvalue is not None:
> oldvalue.delete()
> getattr(target, key).append(value)
>
> return rel
>
>
> class User(Base):
> __tablename__ = 'users'
>
> id = Column(Integer, primary_key=True)
>
>
> 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('user_id', Integer, ForeignKey('users.id'))
>
> def delete(self):
> self.deleted = True
>
>
> User.address = soft_deleting_relationship(
> Address,
> primaryjoin=lambda: and_(Address.user_id == User.id,
> ~Address.deleted),
> )
>
>
> 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()
>
> a2 = Address(email='bar')
> u.address = a2
> sess.commit()
>
> assert a1.user_id == 1, a1.user_id
> assert u.address.id == a2.id
> assert a2.id is not None
> assert a1.deleted
>
>
> test()
>
>
>
--
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The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
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