On Fri, 5 Jul 2013, Chris Angelico wrote:
Oh. Uhm... ahh... it would have helped to mention that it also has a
commit() method! But yes, that's correct; if the object expires (this
is C++, so it's guaranteed to call the destructor at that close brace
- none of the Python vagueness about when __del__ is called) without
commit() being called, then the transaction will be rolled back.
If one wants to duplicate this kind of behavior in Python, that's what
context managers are for combined with a `with` block, which does
guarantee that the __exit__ method will be called - in this case it could
be something as simple as:
from contextlib import contextmanager
@contextmanager
def new_transaction(conn):
tran = conn.begin_transaction()
yield tran
if not tran.committed:
tran.rollback()
Which you would then use like:
conn = create_conn()
with new_transaction(conn) as tran:
rows_affected = do_query_stuff(tran)
if rows_affected == 42:
tran.commit()
And then you get the desired constructor/destructor behavior of having
guaranteed that code will be executed at the start and at the end. You can
wrap things in try/catch for some error handling, or write your own
context manager class.
HTH,
Wayne
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