Re: undefined behaviour for sub-transactions?

On Tue, Nov 29, 2005 at 10:50:01AM -0800, Tyler MacDonald wrote:
> Tim Bunce <Tim(dot)Bunce(at)pobox(dot)com> wrote:
> > I'll guess that what you're really after is to be able to call begin_work
> > again whilst an earlier begin_work is in effect and have the DBI keep a
> > counter of how deeply nested the begin_work calls are. Then commit would
> > decrement the counter and only commit at the outer most level.
> >
> > If you really want that then it's straightforward to implement via a
> > subclass.
>
> This has been done. I'm only using it in two other packages so far,
> but both those and it's own unit tests seem to work well.
>
> http://search.cpan.org/~CRAKRJACK/DBIx-Transaction-0.001/
>
> I've got some ideas for enhancements too, but those are a bit more
> vauge. One of them is that there's differences in transaction behaviour
> across drivers when a query within a transaction fails. eg; under
> PostgreSQL, doing a SELECT on a table that doesn't exist poisons the rest of
> the transaction, whereas under MySQL and SQLite2 the transaction is allowed
> to continue.

PostgreSQL is non-standard (and inconvenient) in this respect.

> There's gotta be some way to wrap this behaviour cleanly so that
> your application can expect the same behaviour regardless of the underlying
> database layer...

There isn't, as far as I know, except to accept the 'lowest common
denominator'. In this case that means forcing a rollback if any
statement fails.

> but this leads to another question :-)
>
> Are all database drivers expected to supply one method to execute a
> query? Eg; do "do", "execute", etc. all always funnel into one core method
> that returns success, error, or exception (if RaiseError) is turned on? Or
> if I wanted to create this functionality and expect it to work under
> multiple database drivers, should I override multiple methods?

execute() is sufficient if the driver doesn't also supply it's own do()
because DBI's default do() calls execute(). But some drivers do supply
their own do() method (for good reasons).

Tim.