Michael Bayer wrote:
> FrancescaL wrote:
>> Hi group,
>>
>> I have a question about Oracle CLOBs.
>>
>> I expect to be able to manage all 3 different LOB column states:
>> (a) Populated
>> (b) Empty
>> (c) NULL
>> First of all: is it my expectation correct?
>
> possibly not. my experience with oracle CLOB is that a "blank" ends up
> being a single blank string.
correction, I meant a "single space", that is, a string of length one
consisting of " ".
>
> SQLAlchemy doesn't do anything here, data is passed directly from
> cx_oracle and back, my advise would be to create a cx_oracle-only test
> case (see the docs on cx_oracle's site, I can't copy and paste a URL on
> this terminal unfortunately) and email the cx_oracle list if you believe
> the DBAPI's direct behavior is erroneous, however this is sort of how it
> goes with Oracle and there might not be a workaround.
>
>
>
>>
>> I'm in process of upgrading to SqlAlchemy 0.6.9 and this seems (to me)
>> no more possible.
>>
>> Here it is how to build 3 examples (one for each column state).
>>
>> # ------------------------------
>> # SQL for manual table creation:
>> DROP TABLE t_tmp_sqla_upgrade;
>> CREATE TABLE t_tmp_sqla_upgrade (
>> id NUMBER (20) not null,
>> text CLOB
>> );
>>
>> # ------------------------------
>> # Python code:
>> from sqlalchemy import MetaData, Table, Column, Integer, Text,
>> create_engine
>> from sqlalchemy.orm import mapper, sessionmaker
>>
>> metadata = MetaData()
>> table = Table('t_tmp_sqla_upgrade', metadata,
>> Column('id', Integer, primary_key=True),
>> Column('text', Text())
>> )
>>
>> class TmpTableEntity(object):
>> pass
>>
>> mapper(TmpTableEntity, table)
>>
>> kwargs = {}
>> kwargs['encoding'] = 'utf-8'
>> engine = create_engine(u"oracle+cx_oracle://user:pwd@db", **kwargs)
>> Session = sessionmaker(bind=engine, autoflush=False)
>>
>> def createItem(session, text):
>> e = TmpTableEntity()
>> e.id = 1
>> e.text = text
>> session.add(e)
>> session.commit()
>> session.expunge_all()
>> return e
>>
>> def readItem(session, id):
>> return
>> session.query(TmpTableEntity).filter(TmpTableEntity.id==id).one()
>>
>> session = Session()
>>
>> # 3 cases (setup and teardown is needed for each case)
>>
>> # Case (a): some text (OK)
>> text = u'some plain ascii text'
>> item = createItem(session, text)
>> rItem = readItem(session, 1)
>> assert rItem.text == text
>>
>> # Case (b): empty text (KO)
>> text = u''
>> item = createItem(session, text)
>> rItem = readItem(session, 1)
>> assert rItem.text == None
>> # But I expect: assert rItem.text == u''
>> # since this is a CLOB field and not a VARCHAR2 one.
>>
>> # Case (c): null text (OK)
>> text = None
>> item = createItem(session, text)
>> rItem = readItem(session, 1)
>> assert rItem.text == None
>>
>> Thank you for your time,
>> Francesca
>>
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>>
>
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