On Sep 20, 2011, at 10:12 AM, Andrei Chirila wrote:
> Hello Michael,
>
> Thank you :)
>
> I changed the code according to your indications:
>
> def paranoid_delete(session, flush_context, instances):
> """ Intercepts item deletions (single item deletions)
> and, if there is a field deleted_at for that
> object, it's updating deleted at instead of really
> deleting the object """
> # print "current session", session
> # print "context", flush_context
> # print "dirty", session.dirty
> # print "deleted", session._deleted
> for obj in session.deleted:
> # print ">> deleted object:", instance, " -> ", obj
> if hasattr(obj, 'deleted_at'):
> print "moving object back: ", obj
> obj.deleted_at = int(time.time())
> session.add(obj)
>
> and it seems to do what it was intended.
>
> Do you know where could I add a hook for before_bulk_delete?
Well since you're subclassing Query I'd add an overriding delete() method to
your LimitingQuery, do your hook in there, then call the delete() method of
Query itself.
>
> Thank you,
> Andrei Chirila
>
>
> On Tue, Sep 20, 2011 at 3:59 PM, Michael Bayer <mike...@zzzcomputing.com>
> wrote:
>
> On Sep 20, 2011, at 8:33 AM, Andrei Chirila wrote:
>
> > Hello,
> >
> > I'm working at implementing a safe delete on my models (having a
> > deleted_at field which is checked and setting a deleted_at field when
> > a model is deleted).
> >
> > I looked over the LimitingQuery recipe and at
> > SessionEvents.before_flush and bellow is my solution. As I'm kind of
> > new SqlAlchemy user, I would like to ask if anyone can see any obvious
> > mistake in the following code (I'm sure I missed bulk deletion and
> > session explunge, but I don't really know how to integrate them).
>
> I'd stay away from identity_map.add(object), as that skips a lot of
> bookkeeping that occurs within the Session. and definitely *never* modify
> anything with an _underscore on Session, your code becomes totally non
> portable to even small changes in SQLAlchemy (which occur frequently as we
> have new releases, bugfixes you'll want, etc). The public (read-only)
> accessor for the "deleted" collection is Session.deleted.
>
> If you have an object marked for deletion, you can re-add it,
> session.add(object), will remove it from the deleted list.
>
> If there's something you need the Session to do that there is not a public
> API for, ask me on the list here first, as I'd rather ensure there are
> maintainable paths for use cases.
>
>
>
>
> >
> > Any feedback would be appreciated.
> >
> > Thank you,
> > Andrei Chirila
> >
> > from sqlalchemy.orm.query import Query
> > import sqlalchemy.event as event
> >
> >
> > class DeletedAtQuery(Query):
> > """ Query adding a default condition that,
> > if deleted_at exists, it should be NULL
> > for the rows returned """
> >
> > def get(self, ident):
> > return Query.get(self.populate_existing(), ident)
> >
> > def __iter__(self):
> > return Query.__iter__(self.private())
> >
> > def from_self(self, *ent):
> > return Query.from_self(self.private(), *ent)
> >
> > def private(self):
> > mzero = self._mapper_zero()
> > if mzero is not None:
> > if hasattr(mzero.class_, 'deleted_at'):
> > crit = mzero.class_.deleted_at == None
> >
> > return self.filter(crit)
> > return self
> >
> >
> > def paranoid_delete(session, flush_context, instances):
> > """ Intercepts item deletions (single item deletions)
> > and, if there is a field deleted_at for that
> > object, it's updating deleted at instead of really
> > deleting the object """
> > # print "current session", session
> > # print "context", flush_context
> > # print "dirty", session.dirty
> > # print "deleted", session._deleted
> > deleted_copy = set(session._deleted)
> > for instance in deleted_copy:
> > obj = instance.obj()
> > # print ">> deleted object:", instance, " -> ", obj
> > if hasattr(obj, 'deleted_at'):
> > # print "moving instance to dirty states"
> > instance.deleted = False
> > obj.deleted_at = int(time.time())
> > session.identity_map.add(instance)
> > del session._deleted[instance]
> >
> >
> > def configure_events(session):
> > """ Helper for applying before_flush hook """
> > event.listen(session, 'before_flush', paranoid_delete)
> >
> > if __name__ == "__main__":
> >
> > import time
> > from sqlalchemy import *
> > from sqlalchemy.orm import *
> > from sqlalchemy.ext.declarative import declarative_base
> >
> > Base = declarative_base()
> >
> > class Group(Base):
> > __tablename__ = 'groups'
> >
> > id = Column(Integer, primary_key=True)
> > name = Column(String)
> > users = relation("User", backref="group", cascade="all")
> >
> > def __repr__(self):
> > return "<Group(%d, %s)>" % (self.id, self.name)
> >
> > class User(Base):
> > __tablename__ = 'users'
> >
> > id = Column(Integer, primary_key=True)
> > name = Column(String)
> > group_id = Column(Integer, ForeignKey('groups.id'))
> > deleted_at = Column(Integer)
> > pets = relation("Pet", backref="user", cascade="all, delete-
> > orphan")
> >
> > def __repr__(self):
> > return "<User(%d, %s)>" % (self.id, self.name)
> >
> > class Pet(Base):
> > __tablename__ = 'pets'
> >
> > id = Column(Integer, primary_key=True)
> > name = Column(String)
> > user_id = Column(Integer, ForeignKey('users.id'),
> > nullable=False)
> > deleted_at = Column(Integer)
> >
> > def __repr__(self):
> > return "<Pet(%d, %s)>" % (self.id, self.name)
> >
> > engine = create_engine("sqlite://", echo=False)
> > Base.metadata.create_all(engine)
> >
> > ClearSession = sessionmaker(bind=engine)
> > Session = sessionmaker(bind=engine, query_cls=DeletedAtQuery)
> >
> > sess = Session()
> > configure_events(sess)
> > clearsess = ClearSession()
> >
> > sess.add_all([Group(name='Group A', users=[
> > User(name='User A1', pets=[
> > Pet(name='Mause A1'),
> > Pet(name='Cat A1')])]),
> > Group(name='Group B', users=[
> > User(name='User B1'),
> > User(name='User B2', pets=[
> > Pet(name='Dog B2'),
> > Pet(name='Mause B2'),
> > Pet(name='Hamster B2')
> > ]),
> > User(name='User B3', pets=[
> > Pet(name='Fish B3'),
> > Pet(name='Snake B3'),
> > Pet(name='Horse B3')
> > ])])])
> >
> > sess.commit()
> >
> > group_a = sess.query(Group).filter(Group.name == 'Group
> > A').first()
> > assert group_a
> >
> > users_in_a = group_a.users
> > assert users_in_a
> > assert len(users_in_a) == 1
> > users_in_a_by_query = sess.query(User).\
> > filter(User.group_id == group_a.id).\
> > all()
> >
> > assert users_in_a_by_query
> > assert len(users_in_a_by_query) == 1
> >
> > pets_in_a = users_in_a[0].pets
> > assert pets_in_a
> > assert len(pets_in_a) == 2
> >
> > # delete one pet
> > pet_id = pets_in_a[0].id
> > sess.delete(pets_in_a[0])
> > sess.commit()
> >
> > pets_in_a = users_in_a[0].pets
> > assert pets_in_a
> > assert len(pets_in_a) == 1
> >
> > pet = clearsess.query(Pet).filter(Pet.id == pet_id).first()
> > assert pet
> > assert pet.deleted_at
> >
> > sess.delete(users_in_a[0])
> > sess.commit()
> >
> > assert len(sess.query(User).\
> > filter(User.group_id == group_a.id).\
> > all()) == 0
> > assert len(clearsess.query(User).\
> > filter(User.group_id == group_a.id).\
> > all()) == 1
> > assert len(sess.query(Pet).all()) == 6
> > assert len(clearsess.query(Pet).all()) == 8
> >
> > group_b = sess.query(Group).filter(Group.name == 'Group
> > B').first()
> > assert group_b
> > assert len(group_b.users) == 3
> >
> > # don't know how to implement batch delete hook yet
> > #sess.query(Pet).delete()
> > #sess.commit()
> >
> > #assert len(sess.query(Pet).all()) == 0
> > #assert len(clearsess.query(Pet).all()) == 8
> >
> > sess.delete(group_b)
> > sess.commit()
> > groub_b_deleted = sess.query(Group).filter(Group.name == 'Group
> > B').first()
> > assert groub_b_deleted is None
> >
> > assert len(sess.query(Pet).all()) == 0
> > assert len(clearsess.query(Pet).all()) == 8
> > assert len(sess.query(User).all()) == 0
> > assert len(clearsess.query(User).all()) == 4
> >
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