how to use session.merge [sqlalchemy]

result

[<__main__.Sub object at 0x1f44250>, <__main__.Sub object at 0x1f44390>, <__main__.Sub object at 0x1f44350>]
[u'a', u'b', u'c']



pre commit
------
	ok
after commit
------
	Parent instance <Main at 0x1f3d190> is not bound to a Session; lazy load operation of attribute 'subs' cannot proceed
session merge
------
	Parent instance <Main at 0x1f3d190> is not bound to a Session; lazy load operation of attribute 'subs' cannot proceed
	ok

session.merge.example.py

import sqlalchemy as sa
import sqlalchemy.orm as orm
import sqlahelper
from sqlalchemy.ext.associationproxy import association_proxy
base = sqlahelper.get_base()

class Main(base):
    id = sa.Column(sa.Integer, primary_key=True)
    name = sa.Column(sa.Unicode(255))
    __tablename__ = "main"
    subbox = association_proxy("subs", "name", creator=lambda name: Sub(name=name))

class Sub(base):
    id = sa.Column(sa.Integer, primary_key=True)
    main_id = sa.Column(sa.Integer, sa.ForeignKey("main.id"))
    main = orm.relationship("Main", backref="subs")
    name = sa.Column(sa.Unicode(255))
    __tablename__ = "sub"
    
engine = sa.create_engine("sqlite://")
sqlahelper.add_engine(engine)
base.metadata.create_all()

session = sqlahelper.get_session()

main = Main(name=u"foo")
main.subbox.append(u"a")
main.subbox.append(u"b")
main.subbox.append(u"c")

def use_lookup(main):
    try:
        main.subs
        print "\tok"
    except Exception, e:
        print "\t%s" % e
        pass

def section(mes):
    print mes
    print "------"

print [s for s in main.subs]
print [s.name for s in main.subs]


print "\n\n"

session.add(main)

section("pre commit")
use_lookup(main)

import transaction
transaction.commit()

section("after commit")
use_lookup(main)

### session.merge
section("session merge")
merged = session.merge(main)
use_lookup(main)
use_lookup(merged)