usersession ShardedQuery bulk delete

------------ model.py ----------------

meta = MetaData()

usersession_table = Table('kg_usersession', meta,
                          Column('session_id', String(32), primary_key=True),
                          Column('user_id', BigInteger, index=True, nullable=False),
                          Column('create_time', DateTime, index=True),
                          Column('expire_time', DateTime, index=True),
                          Column('site', String(10)),
                          mysql_engine='MyISAM'
                          )

class UserSession(object):
    
    def __init__(self):
        self.session_id = ''
        self.user_id = None
        self.create_time = None
        self.expire_time = None
        self.site = ''

usersession_shard_engines = {}
for i in range(settings.DB_USERSESSION_SHARD_MOD):
    usersession_shard_engines[i] = create_engine(settings.DB_USERSESSION_URI+'_%d?charset=utf8'%i, encoding='utf-8', convert_unicode=True, pool_size=settings.DB_POOL_SIZE, pool_recycle=settings.DB_POOL_RECYCLE_TIMEOUT, echo=settings.DEBUG)

create_usersession_session = sessionmaker(class_=ShardedSession, expire_on_commit=False)
create_usersession_session.configure(shards=usersession_shard_engines)

def shard_value(value):
    return int(value, 16) % settings.DB_USERSESSION_SHARD_MOD

def shard_chooser(mapper, instance, clause=None):
    if instance:
        return shard_value(instance.session_id)

def id_chooser(query, ident):
    return [ i for i in range(settings.DB_USERSESSION_SHARD_MOD) ]

def query_chooser(query):
    ids = []
    
    for column, operator, value in get_query_comparisons(query):
        if column.shares_lineage(usersession_table.c.session_id):
            if operator == operators.eq:
                if value:
                    ids.append(shard_value(value))
            if operator == operators.in_op:
                ids.extend([ shard_value(v) for v in value if v ])
    
    if len(ids) == 0:
        return [ i for i in range(settings.DB_USERSESSION_SHARD_MOD) ]
    else:
        return ids

create_usersession_session.configure(shard_chooser=shard_chooser,
                                     id_chooser=id_chooser,
                                     query_chooser=query_chooser)

mapper(UserSession, usersession_table)

--------------- bulk_delete.py ------------------

    session = create_usersession_session()
    session.query(UserSession).filter(UserSession.expire_time<=expire_time).delete();
    session.close()