On Jan 30, 2010, at 9:07 AM, avdd wrote:
> I'm using session.add() to refresh my objects while working on them,
> because I don't want to merge them with the persistent state. But it
> appears deletes aren't carrying across to child relations:
this example is too compliated for me to understand without great effort,
perhaps someone else has the time to follow it more closely - it appears to be
creating and closing many new sessions and add()ing objects between them - an
unusual series of events. The policy of add() is that it puts an object in
the session. If its already there, nothing happens. It doesnt invalidate any
state or reconcile with what's currently visible in the transaction, so if the
example is attempting to illustrate, "transaction A changed a row, but
transaction B doesn't see it!", you'd have to expire the appropriate parts of
session B for those changes to be seen.
>
>
> $ cat listdelete.py; python listdelete.py
>
> import sqlalchemy as sql
> from sqlalchemy import orm
> from sqlalchemy.ext.declarative import declarative_base
>
> echo = 0
> engine = sql.create_engine("sqlite:///:memory:", echo=bool(echo))
> metadata = sql.MetaData(bind=engine)
> DB = orm.sessionmaker(bind=engine)
> T = declarative_base(metadata=metadata)
>
> class A(T):
> __tablename__ = 'a'
> id = sql.Column(sql.Integer, primary_key=True)
> info = sql.Column(sql.String)
> cc = orm.relation('C',
> backref='a',
> cascade='all,delete-orphan')
> def __repr__(self):
> return " >> a: %s cc=%s" % (self.info, len(self.cc))
>
> class C(T):
> __tablename__ = 'c'
> a_id = sql.Column(sql.Integer, sql.ForeignKey('a.id'),
> primary_key=True)
> i = sql.Column(sql.Integer, primary_key=True)
>
> def get():
> return DB().query(A).first()
>
> def change(a, s, i):
> orm.object_session(a).close()
> db = DB()
> db.add(a)
> a.info = s
> del a.cc[-1]
> a.cc.append(C(i=i))
> db.close()
>
> metadata.create_all()
> A.__table__.delete().execute()
>
> db = DB()
> a = A(id=1, info='blah', cc=[C(i=1), C(i=2)])
> db.add(a)
> db.commit()
> db.close()
>
> print get()
>
> # merge and flush
> a = get()
> change(a, 'change one', 3)
> db = DB()
> db.merge(a)
> db.commit()
> db.close()
>
> print get()
>
> # add and flush
> a = get()
> change(a, 'change two', 4)
> db = DB()
> db.add(a)
> db.commit()
> db.close()
>
> print get()
>
>
>>> a: blah cc=2
>>> a: change one cc=2
>>> a: change two cc=3
>
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