sqlalchemy mapper event issue
class User(Base):
    __tablename__ = 'user'
    userId = Column(Integer, primary_key=True)
    email = Column(String(60), unique=True,nullable=False)
    userName = Column(Unicode(16),unique=True)
    _password = Column('password', Unicode(60))
    groups = relationship("Group",secondary='userGroup')
    profile = relationship("UserProfile",uselist=False,backref='user')

class Group(Base):
        __tablename__ = 'group'
        groupId = Column(Integer,
                       Sequence('group_id_seq', optional=True),
                       primary_key=True)
        groupName = Column(Unicode(255), unique=True)

UserGroupTable = Table('userGroup', Base.metadata,
        Column('userId', Integer, ForeignKey(User.userId)),
        Column('groupId', Integer, ForeignKey(Group.groupId))
    )


class UserProfile(Base):
    __tablename__='userProfile'
    userId = Column(Integer, ForeignKey('user.userId'), primary_key=True)
    dateJoin = Column(Date,nullable=False,default=func.current_date())
    gender = Column(Integer)

def before_insert_user_listener(mapper,connection,target):
    session=DBSession()
    ug=session.query(Group).filter(Group.groupName=='user').first()
    target.groups.append(ug)
    target.profile=UserProfile()
    log.debug(">>>>>")

def initialize_sql(engine):
    DBSession.configure(bind=engine)
    Base.metadata.bind = engine
    Base.metadata.create_all(engine)
    try:
        session = DBSession()
        #event register
        event.listen(User,'before_insert',before_insert_user_listener)
        group1 = Group('admin')
        group2 = Group('user')
        session.add(group1)
        session.add(group2)
        transaction.commit()
    except IntegrityError:
        pass

def my_before_commit(session):
    g=session.query(Group).filter(Group.groupName=='user').one()
    for target in session:
        if isinstance(target, User) and target in session.new:
            target.groups.append(ug)