Am 04.03.2011 um 22:44 schrieb demitri:
On Mar 1, 5:04 pm, "Diez B. Roggisch" <[email protected]> wrote:
A scoped session is a factory for the actual sesion - but you can use
it directly, for that thread, there will be a local instance. So it's
perfectly fine to call DBSession.<whatever>, it should work.
Thank - I'll give that a try.
The confusing thing from the tutorial here:
http://turbogears.org/2.0/docs/main/Wiki20/wiki20.html
is the use of transaction. When does the transaction begin - during
"import transaction"? Is there a reason to use this over
def index:
session = DBSession()
...
session.commit()
you confuse a few things here.
First of all, a transaction in SQLAlchemy is begun implicitly. You
never call begin(). But this is not done through import - how could it
be, you don't know your database configuration during import!
Second, the example you show doesn't really apply, because it's about
setting up the application for testing or initial boot-strapping. It's
*not* what happens during a normal application run.
So it's next to irrelevant for this discussion.
What happens in TG2 is this:
- through the ZopeTransactionExtension, SQLAlchemy's Session is
hooked into the transaction-modules begin/commit/abort-functions
- through repoze.tm2, there is a middleware generated that on each
request will begin a transaction (as explained above, in SA a NOP),
and when the request ends, it will commit or rollback - depending on
either doom() being called, or an exception not being caught, or a
normal run.
- inside your controller, you never ever can run begin/commit/
rollback. You can only doom a transaction.
- the last point is not 100% true - you can use commit/rollback your
own, but only if your database supports sub-transactions. Then, the
begin() is actually not a NOP.
But usually, that's not what you do. Instead, you write code that
- properly checks before jumping,as e.g. violating a unique-
constraint will abort the transaction
- locks, if needed
HTH,
Diez
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