我通过网络将 sqlalchemy 对象发送到另一台机器。首先我将它序列化为一个字符串，然后加密并发送。我用以下方式序列化它：
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker, scoped_session
from sqlalchemy.ext.serializer import loads, dumps
engine = create_engine(connection_str)
S = scoped_session(sessionmaker(bind=engine, expire_on_commit=False))
session = S()
data = session(MyObj).all()
serialized = pickle.dumps([dumps(d) for d in data])
crypted = crypt(serialized) #encrypting the serialized data
send(machine, crypted) #sending encripted data to 'machine'
在另一台机器上：
encrypted = get_data()
serialized = decrypt(encrypted)
data = [loads(d, Base.metadata, S) for d in pickle.loads(serialized)]
for d in data:
session.merge(d)
session.commit()
但它抛出：(IntegrityError) node_type.id may not be NULL u'INSERT INTO myobj (col1, col2) VALUES (?, ?)' (None, None)
当我尝试打印时data它会抛出：DetachedInstanceError Instance <MyObj at 0x24e0c70> is not bound to a Session; attribute refresh operation cannot proceed
或：ObjectDeletedError
问题是什么？
此处：
如何从 SqlAlchemy 创建和恢复备份？被告知那session.merge()会很好，但它对我不起作用。