[Lazarus] What is a TSQLTransaction and why do I need one?

[Joost van der Sluis]

On Mon, 2010-11-29 at 17:57 +0100, michael.vancanneyt at wisa.be wrote:
> 
> On Mon, 29 Nov 2010, Joost van der Sluis wrote:
> 
> > On Wed, 2010-11-24 at 20:57 +0100, Michael Van Canneyt wrote:
> >>
> >> On Wed, 24 Nov 2010, Alexsander Rosa wrote:
> >>
> >>> But it is transparent to the libpq programmer; why it's not transparent with sqldb?
> >>
> >> Correction: it can be transparant in libpq.
> >>
> >> But we can make it so in SQLDB.
> >>
> >> The SQLDB model is in fact modeled after Firebird.
> >> Firebird offers more control over the transactions.
> >>
> >> We did not want to take away this possibility, so we modeled sqldb on
> >> the most powerful RDBMS. This adds some overhead for the others.
> >>
> >> What we neglected to do is add what Martin added: offer a less intrusive
> >> way for the programmer to use it (i.e. create a default transaction in the
> >> background if none is specified, and close the transaction once the data
> >> is read).
> >>
> >> But we'll do that too, all in good time.
> >>
> >> If someone is in a hurry, patches are definitely accepted.
> >
> > Problem is that I haven't found a good model for this. Martin's solution
> > could be an idea, though.
> >
> > It could help if someone could sketch the typical wanted behavior from
> > the transactions.
> 
> I sent an idea for an implementation in a reply to Alexsander Rosa.
> basically:
> 
> TConnectionOption = (coAutoTransaction)
> TConnectionOptions = set of TConnectionOption;
> 
> Property TSQLConnection.options = TConnectionOptions;
> 
> Procedure TSQLConnection.CreateDefaultTransaction;
> 
> If coAutoTransaction is set, and TSQLQuery does not have a TSQLTransaction
> assigned, it creates one through TSQLConnection.CreateDefaultTransaction.
> (It should be of type TSQLAutoTransaction, a simple descendent of
> TSQLtransaction, so detection of 'default transaction' is simple)
> 
> Whenever a TSQLQuery statement is executed and the transaction of TSQLTransaction is
> of type TSQLAutoTransaction, then it automatically commits (more flags can be introduced
> for this).

This doesn't change Alexsander problem, because there's still the same
transaction. Only difference is that he doesn't have to place it on the
form.

Besides that, I think that disabling the explicit transaction for
Postgres can be done much easier. I have to read the documentation
again, but my guess is that if you pass a nil pointer for the
transaction, it will use an implicit transaction. So the only change
would be to remove the check if an exception is assigned...

But first I want to know what the problem is we solve with this. And if
it's worth the effort/extra overhead.

Joost.