On Jan 26, 2011, at 7:47 PM, Michael Bayer wrote:
>
> On Jan 26, 2011, at 6:32 PM, A.M. wrote:
>
>> Well, I spoke too soon :( What is the mistake in the following sample code
>> which causes the COMMITs to be emitted? Setting autocommit to either True or
>> False emits the same SQL. I think this is a case of staring at the same code
>> too long causing brain damage- thanks for your patience and help!
>>
>> from sqlalchemy.engine import create_engine
>> from sqlalchemy.orm.session import sessionmaker
>> from sqlalchemy.orm import scoped_session
>> from sqlalchemy.schema import DDL,MetaData,Table
>>
>> engine = create_engine('postgresql://localhost/test',echo=True)
>> session = scoped_session(sessionmaker(bind=engine))
>> metadata = MetaData()
>> metadata.bind = engine
>>
>> Table('test1',metadata)
>> Table('test2',metadata)
>> metadata.create_all()
>
> metadata.create_all() looks at the "bind" attribute, then uses it to execute
> each DDL statement. The "bind" here is an engine so it uses connectionless
> execution. connectionless execution is usually autocommit as documented
> here:
> http://www.sqlalchemy.org/docs/core/connections.html#connectionless-execution-implicit-execution
>
> to emit create_all() in a transaction:
>
> conn = engine.connect()
> with conn.begin():
> metadata.create_all(conn)
Ugh- thanks for being patient with a noob- I had erroneously assumed that the
creation of a session would assume responsibility for transaction management
like the zope transaction handler. It makes sense now that the session is
exclusively specific to ORM management- the section "Joining a Session into an
External Transaction" helped to clear things up- there is indeed some
interaction between connection and session transactions.
Cheers,
M
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