Question

Im sending sqlalchemy objects trough net to another machine. First I serialize it to a string, then crypting and sending.
I serialize it with:

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'

and on the other machine:

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()

but it throws: (IntegrityError) node_type.id may not be NULL u'INSERT INTO myobj (col1, col2) VALUES (?, ?)' (None, None)

and when i try to print the data it throws: DetachedInstanceError Instance <MyObj at 0x24e0c70> is not bound to a Session; attribute refresh operation cannot proceed
or an:ObjectDeletedError

what is the problem?

here:
How to create and restore a backup from SqlAlchemy? is told that session.merge() would be fine, but it didnt work for me.

Answer 1

From the docs for sqlalchemy.ext.serializer:

“The serializer module is only appropriate for query structures. It is
not needed for […] instances of user-defined classes”

Maybe try to just use pickle and not sqlalchemy.ext.serializer for this use case.